The  National 
Electrical  Code. 


AN  ANALYSIS  AND  EXPLANATION  OF  THE 

UNDERWRITERS'  ELECTRICAL  CODE, 

INTELLIGIBLE  TO  NON-EXPERTS. 


PIERCE  and  RICHARDSON, 

|    V 

ELECTRICAL  ENGINEERS. 
CHICAGO. 


PUBLISHED    BY 

CHARLES  A,  HEWITT,   510  ROYAL  BUILDING, 

CHICAGO,   ILL. 


COPYRIGHTED  1896 

BY 
CHARLES  A.   HEWITT. 


Publisher's  Announcement. 


In  response  to  many  requests,  the  notable  articles 
on  "The  National  Electrical  Code,"  by  Pierce  and 
Richardson,  in  "The  Insurance  Post "  of  Chicago,  have 
been  revised  and  extended  and  are  published  herewith 
in  convenient  book  form.  As  stated  in  the  sub-title, 
this  little  book-  is  "An  Analysis  and  Explanation  Of 
The  Underwriters'  Electrical  Code,  Intelligible  to  Non- 
Experts."  Most  writers  on  electrical  topics  confuse 
the  non-expert  by  their  continued  use  of  technical 
terms.  Messrs.  Pierce  and  Richardson,  whose  com- 
petency is  unquestioned,  have  undertaken  "to  explain 
the  matter  in  ordinary  language, "for  the  special  benefit 
of  insurance  inspectors  and  electrical  students.  Hence, 
also,  the  common  analogies  and  simple  definitions. 

On  the  authority  of  eminent  electricians,  the  Un- 
derwriters' Code  is  to-day  the  best  guide  to  safe  con- 
struction and  certain  provision  against  loss  by  fire. 
The  joint  work  of  advanced  underwriters  and  expe- 
rienced electricians,  it  represents  years  of  patient  re- 


iv.  PUBLISHER'S  ANNOUNCEMENT. 

search  and  the  accumulated  knowledge  of  recognized 
experts.  A  study  of  its  rules  and  requirements  has 
been  often  urged  upon  central  station  men  and  engi- 
neers. Insurance  companies  and  their  representatives, 
meanwhile,  have  come  to  look  to  the  Code  for  instruc- 
tion and  guidance,  but  without  knowing  why  or  where- 
fore. The  whys  and  wherefores  are  clearly  set  forth 
in  the  following  pages;  and  now  that  Electricity  is 
coming  into  general  use,  the  necessity  of  a  better 
knowledge  of  electrical  hazards  is  freely  admitted  by 
all  those  engaged  in  fire  insurance. 

Supplemental  to  the  general  exposition,  properly 
classified  and  indexed,  is  the  "Appendix,' '  in  which 
will  be  found  tables  and  curves  for  measuring  wires, 
and  the  full  text  of  the  Underwriters'  National  Elec- 
trical Code  for  1896.  The  writings  of  Messrs.  Pierce 
and  Richardson,  it  is  proper  to  add,  have  attracted  the 
'  favorable  notice  of  prominent  underwriters,  architects, 
builders  and  engineers.  It  is  believed  that  this  little 
book  will  prove  indispensable  to  most  insurance  in- 
spectors and  special  agents,  and  of  practical  interest 
and  value  to  many  electricians. 

C.   A.    H. 
CHICAGO,  NOVEMBER,  1896. 


TABLE  OF  CONTENTS. 


CHAPTER  I. 

PAGES. 

INTRODUCTORY  AND  DEFINITIONS  OF  ELECTRICAL  TERMS 

The  National  Code  —  Electricity  —  Electro-Motive  Force 

—  Potential  or  Pressure — Dynamo — Conductor — Re 
sistance  —  Insulator — Polarity,       .  .  .         g  to  18 

CHAPTER  II 

CENTRAL  STATIONS  FOR  LIGHT  AND  POWER       PART  I. 

Central  Station  —  Generators  —  Care  and  Attendance  — 
Conductors  —  Switchboards,  .  19  to  27 

CHAPTER  III 

CENTRAL  STATIONS  FOR  LIGHT  AND  POWER.  PART  II 
Switchboards  Their  Location  and  Construction  —  Resist- 
ance Boxes  and  Equalizers  Their  Uses  and  How  Installed 

—  Lightning  Arresters,  Why  Needed  and  Where  to  Place 
Them,  .         28  to  35 

CHAPTER  IV 

CENTRAL  STATIONS  FOR  LIGHT  AND  POWER.  PART  III. 
Testing  — Series  Circuits  —  Multiple-arc  Circuits — Al- 
ternating Circuits  —  Motors  .  36  to  46 

CHAPTER  V. 
CLASS  B,  HIGH  POTENTIAL  SYSTEMS      PART  I 

High  Potential  Circuits  —  Outside  Conductors  —Class  of 
Wire  Allowed  —  Crosses — Wires  Entering  Buildings  — 
Switches  —  Interior  Conduits  —  Insulation  of  Wires  — 
List  of  Approved  Wires  —  Joints  in  Wires,  .  47  to  55 


VI.  TABLE    OF    CONTENTS. 

CHAPTER  VI. 

PAGES. 

HIGH  POTENTIAL  SYSTEMS.     PART  II. 

Arc  Lamps  —  Spark  Arresters  —  Hanger  Boards  — Auto- 
matic Switches  —  Suspension  of  Arc  Lamps  —  Incandes- 
cent Lamps  on  Series  Arc  Circuits  —  Definition  of  "  Mul- 
tiple Series"  and  "Series  Multiple,"  .  56  to  65 

CHAPTER  VII 
CLASS  C.  Low  POTENTIAL  SYSTEMS.     PART  I 

Two  and  Three  Wire  Systems  —  Outside  Conductors  — 

"Constant  Current"  and   "Constant  Pressure      Sys 

terns — Fusible  Cut-outs,  .  .         66  to  72 

CHAPTER  VIII. 
CLASS  C    Low  POTENTIAL  SYSTEMS.     PART  II. 

Underground  Conductors  —  Inside  Wiring,  General  Rules 

—  Insulation  of  Wires  — Minimum  Size  of  Wires  —  Tubes 
or  Bushings  —  Protection  of  Low  Potential  from  High 
Potential  Wires  —  Joints  in  Wires  and  in  Insulation,     73  to  83 

CHAPTER  IX. 
CLASS  C   Low  POTENTIAL  SYSTEMS.     PART  III. 

Special  Rules  —  Wiring  Not  Encased  in  Moulding  or 
Approved  Conduit  —  Various  Methods  of  Running  Wires 

—  Methods  Permitted  by  the  Code,  .         84  to  90 

CHAPTER  X 
CLASS  C,  Low  POTENTIAL  SYSTEMS.     PART  IV. 

Mouldings  —  Special  Wiring  in  Breweries,  Packing 
Houses,  Stables  Dye  Houses,  Pulp  Mills,  etc.,  91  to  96 

CHAPTER  XI 
CLASS  C,  Low  POTENTIAL  SYSTEMS      PART  V. 

Interior  Conduits.  Their  Object  and  Their  Evolution  — 
How  They  Should  be  Installed,  .  .  97  to  105 


TABLE    OF    CONTENTS.  VII. 

CHAPTER  XII 

PAGES. 

CLASS  C,  Low  POTENTIAL  SYSTEMS      PART  VI 

Safety  Cut-outs  —  A  System  of  Conductors  —  How  Pro- 
tected by  Cut-outs  —  Double -pole  Cut-outs  —  Fuse 
Blocks,  .  .  .  106  to  113 

CHAPTER  XIII 

CLASS  C,  Low  POTENTIAL  SYSTEMS      PART  VII. 

Cut-outs  and  Cut-out  Boxes—  Maximum  Safe  Carrying 
Capacity  of  Wires,  (Table)  —  The  Heating  of  Wires  Car- 
rying Electric  Currents,  .  114  to  123 

CHAPTER  XIV. 
CLASS  C,   Low  POTENTIAL  SYSTEMS.     PART  VIII. 

Switches  —  Snap  Switches  —  Fixtures  —  Combination 
Fixtures,  .  .  .  124  to  131 

CHAPTER   XV. 
CLASS  C,  Low  POTENTIAL  SYSTEMS.     PART  IX. 

Arc  Lamps  on  Low  Potential  Systems  —  Electric  Gas 
Lighting  —  Lamp  Sockets  —  Flexible  Cord,  .  132  to  139 

CHAPTER  XVI. 

CLASS  D,  ALTERNATING  SYSTEMS,  CONVERTERS  OR  TRANSFORMERS. 
Direct     and    Alternating    Currents  —  Transmission    of 
Energy   by    Electricity  —  Transformers  —  Primary   and 
Secondary  Circuits  —  Transformers  in  Buildings,    140  to  149 

CHAPTER  XVII. 
CLASS  E,  ELECTRIC  RAILWAYS. 

Ground  Return  —  Circuit  Breakers  —  Bonds  —  Lighting 
and  Power  from  Railway  Circuits  —  Electrolysis,  150  to  156 

CHAPTER  XVIII. 
CLASS  F,  STORAGE  OR  PRIMARY  BATTERIES. 

Description  of  Primary  and  Secondary  Batteries  — 
Points  to  be  Observed  in  Installation  of  Storage  Bat- 
teries, ....  157  to  164 


VIII.  TABLE    OF    CONTENTS. 

CHAPTER  XIX. 

PAGES. 

MISCELLANEOUS. 

Insulation  —  Insulation  Resistance  —  Dead  Ground  — 
Short  Circuit  —  Insulation  Resistance  Required  by  Code, 
(Table)— Ground  Wires— Protection  of  Telephone,  Clock 
and  Similar  Circuits  —  How  to  Secure  High  Insula- 
tion, .  165  to  174 

CHAPTER    XX. 
EDITION  OF  1896. 

General  Suggestions  —  Changes  from  Code  of  1895  — 
Grounding  of  Frames  of  Direct  Coupled  Generators  — 
Lightning  Arresters  —  Motors  —  Weather-proof  Wire  — 
Interior  Conduits  —  Closed  Arc  Lamps,  .  175  to  182 

CHAPTER  XXI. 
EDITION  OF  1896. 

Changes  from  Code  of  1895  — Mechanical  Protection  of 
Wires  —  Mouldings  —  Iron-armored  Conduit  —  Fixture 
Work  —  Flexible  Cord  —  Decorative  Series  Lamps  — 
Transformers  in  Buildings  —  Car  Houses — Electric 
Heaters  —  New  List  of  Approved  Wires  —  The  Object 
and  Limitations  of  the  Code,  .  .  183  to  196 

APPENDIX  —  TABLES  AND  CURVES,         .  .-     197  to  200 

APPENDIX  (CONTINUED)  —  FULL  TEXT  OF  THE  UNDERWRITERS 

NATIONAL  ELECTRICAL  CODE,     .  .        201  to  222 


The  National  Electrical  Code, 


CHAPTER    I. 

INTRODUCTORY    AND    DEFINITIONS    OF   COMMON    TERMS. 

With  the  exception  of  those  who  are  directly  engaged 
in  electrical  employments,  or  are  investing  their  money 
in  electrical  plants  or  enterprises,  no  one  has  a  more 
direct  interest  in  the  proper  construction  of  electrical 
work  than  the  representatives  of  insurance  companies. 
To-day  the  insurance  agent  duly  appreciates  if  he  does 
not  even  overestimate,  the  hazard  that  may  be  caused 
by  faulty  electrical  construction.  How  to  recognize 
this  hazard  when  he  sees  it,  and  how  to  avoid  it,  is, 
however,  a  difficult  and  often  an  unsolved  problem. 
When  the  question  of  safety  is  one  of  ordinary  building 
construction,  the  hazard  is  easily  seen,  when  once  it 
has  been  pointed  out,  and  the  remedy  is  usually  as 
easily  described  and  understood.  When  we  come  to 
electrical  matters,  however,  we  often  find  that  the  mind 
of  nearly  every  one,  except  the  so-called  electrical 
expert,  is  more  or  less  befogged.  An  explanation  does 


10  THE    NATIONAL    ELECTRICAL    CODE. 

not  always  explain,  and  even  when  one  concludes  that 
he  has  obtained  a  clear  and  satisfactory  understanding 
of  a  hazard  and  its  remedy,  he  is  straightway  confronted 
with  some  astounding  statement  or  some  apparently 
mysterious  phenomena. 

It  has  occurred  to  us  that  possibly  the  principal  reason 
why  most  persons  have  such  an  indefinite  knowledge  of 
even  the  simple  things  in  the  application  of  electricity 
is,  that  electricity  has  almost  a  language  of  its  own. 
Every  description  of  anything  electrical  by  an  electri- 
cian, is  filled  with  such  terms  as  "volts,"  "amperes," 
"ohms,"  "rheostats,"  "induction,"  "electro-motive 
force,"  etc.,  etc.  Every  day  adds  new  words  to  this 
peculiar  vocabulary,  so  that  even  the  electrical  engineer 
has  to  be  well-read,  to  keep  track  of  all  these  electrical 
terms.  A  good  sized  electrical  dictionary  has  already 
been  published,  but  this  would  have  to  be  revised  as 
often  as  the  Chicago  city  directory  to  keep  up  with  the 
inventive  genius  of  the  men  who  coin  electrical  terms. 
While  these  electrical  terms  are  useful  and  necessary, 
still  it  seems  to  us  that  their  great  number  has  discour- 
aged many  from  the  study  of  practical  things  which 
they  wish  to  know,  and  which  are  easily  understood  if 
expressed  or  explained  in  common,  every-day  language. 
It  is  our  intention  in  this  and  succeeding  chapters,  to 
discuss  that  part  of  electrical  construction  which  has  a 
direct  bearing  on  the  question  of  safety,  and  it  will  be 
our  aim  to  do  this,  as  far  as  is  possible,  in  ordinary 
language,  avoiding  technical  expressions  when  we  can, 
and  when  they  cannot  be  avoided,  as  must  often  be  the 
case,  we  shall  try  to  give  a  simple  explanation  or 


DEFINITIONS    OF    COMMON    TERMS.  II 

definition  of  the  expressions,  not  going  into  a  scientific 
discussion,  or  trying  to  give  definitions  which  shall  be 
logically  and  mathematically  precise,  but  simply  giving 
such  explanation  as  will,  we  hope,  enable  the  unscien- 
tific reader  to  form  a  conception  of  what  is  going  on  in 
a  system  of  electrical  wires,  and  to  see  clearly  why  one 
thing  is  safe  and  another  is  not. 

We  do  not  propose  to  assume  that  the  reader  knows 
anything  at  all  about  electricity,  and  we  offer  our  apol- 
ogies right  here  to  any  who  may  feel  that  their  intelli- 
gence is  insulted.  We  also  apologize  to  those  who  have 
struggled  to  explain  the  same  thing  in  technical  language 
and  mathematical  formulae,  for  our  audacity  of  under- 
taking a  task  at  which  so  many  of  them  have  been 
unsuccessful.  We  are  not  prompted  by  conceit  in  our 
undertaking.  Like  all  who  have  long  been  engaged  in 
electrical  work,  we  have  been  met  daily,  for  years,  with 
questions  of  all  kinds  from  men  who  had  no  time  to 
study  technical  works,  but  who  wanted  a  simple  expla- 
nation of  something  electrical.  Usually  we  have  been 
able  to  explain  the  matter  in  question  in  ordinary 
language  to  the  satisfaction  of  the  inquirer,  and  often 
we  have  had  a  man  go  away  with  the  knowledge  of  the 
subject  which  answered  his  purpose  perfectly,  and  was 
doubtless  infinitely  more  satisfactory  to  him  than  our 
understanding  was  to  us.  We  feel,  therefore,  that  our 
undertaking  is  a  laudable  one,  and  if  our  success  is  not 
equal  to  our  expectation,  we  hope  that  we  shall,  at 
least,  help  to  open  a  path  for  others.  It  is,  of  course, 
impossible  in  this  book,  to  cover  the  entire  field 
of  electrical  construction  or  even  the  applications  of 


12  THE    NATIONAL    ELECTRICAL    CODE. 

electricity  that  might  interest  our  readers.  We  have, 
therefore,  decided  to  take  up  the  subject  purely  from 
the  insurance  man's  point  of  view.  We  shall  consider 
only  electricity  as  it  may  or  may  not  create  a  hazard. 

This  subject  has  been  carefully  and  very  completely 
covered  in  the  rules  known  as  the  "National  Code." 
This  code  in  its  original  form,  or  as  revised  and  incor- 
porated into  the  regulations  of  the  various  insurance 
associations,  is  familiar  to  every  one  in  insurance  lines. 
It  is,  however,  condensed  in  form,  and  full  of  technical 
terms.  We  have,  therefore,  thought  it  proper  to  take 
this  code  as  our  text.  We  shall  endeavor  to  explain 
the  code  in  every-day  language,  giving  such  definitions 
and  explanations  as  will,  we  hope,  enable  any  one  to 
understand  its  meaning  without  the  assistance  of  an 
electrical  dictionary  or  electrical  text  books.  We  shall 
take  up  the  various  points  in  the  same  order  that  they 
are  taken  up  in  the  code.  The  National  Code  is  the 
outcome  of  experience.  It  is  the  result  of  a  great 
amount  of  study  and  discussion.  It  stands  to-day  as 
the  best  expression  of  what  is  definitely  believed  by  the 
ablest  men  of  both  insurance  and  electrical  lines,  and 
if  we  shall  succeed  in  assisting  any  one  to  a  better 
understanding  and  appreciation  of  its  principles,  \ve 
shall  feel  repaid  for  our  efforts.  The  following  defini- 
tions are  absolutely  necessary  to  describe  the  most 
common  terms  which  constantly  appear  in  the  code. 

Electricity. — We  do  not  know  what  electricity  is,  and 
it  is  useless  for  us  to  try  to  define  it.  We  perceive  it  as 
a  manifestation  of  energy.  All  we  need  to  know  of  its 
nature  for  our  present  use,  is  that  we  can  transform  the 


DEFINITIONS    OF    COMMON    TERMS.  13 

work  of  an  engine  or  water-wheel  into  electricity,  and 
that  we  can  direct  and  regulate  its  distribution  by  wires 
or  conductors,  and  transform  it  again  into  energy  in 
the  form  of  light,  heat,  or  work,  in  moving  a  machine. 
There  is  but  one  kind  of  electricity,  as  far  as  we  know, 
but  it  manifests  itself  to  us  in  various  ways.  In  the 
production  of  light,  heat  and  power,  we  deal  only  with 
dynamical  electricity,  or  electricity  in  motion. 

Electric  Current. — While  we  have  to  deal  with  elec- 
tricity in  motion,  still,  as  its  nature  is  not  known,  its 
motion  is  but  imperfectly  understood.  It  is  necessary 
for  us,  however,  to  have  some  theory  to  account  for  its 
actions.  For  all  ordinary  purposes,  we  may  consider 
electricity  to  be  a  fluid,  and  to  have  a  motion  in  a  wire 
like  water  in  a  pipe.  Following  this  analogy,  we  speak 
of  a  "current"  of  electricity.  As  with  water  in  a  pipe 
or  a  river,  so  with  electricity,  the  amount  of  flow  is 
proportional  to  the  strength  of  the  current,  and  to  the 
time  during  which  it  flows.  The  rate  of  flow  of  elec- 
tricity is  called  "the  current  strength,"  or,  more  com- 
monly, the  "current"  It  is  measured  by  an  arbitrary 
standard  called  an  "ampere."  The  ampere  is  the  unit 
of  current  strength.  The  total  amount  of  electricity 
flowing  will,  of  course,  be  measured  in  "ampere  hours." 
For  example,  an  ordinary  2,000  c.  p.  arc  lamp,  such  as 
is  commonly  used  in  street  illumination,  requires  a  cur- 
rent of  10  amperes.  If  the  lamp  burns  for  10  hours, 
the  total  amount  of  current  consumed  will  be  100 
ampere  hours.  When  we  speak  of  a  wire  carrying  a 
current  of  10  amperes,  we  mean  that  10  units  of  current 
are  flowing  in  the  wire,  and  we  use  the  expression  in 


14  THE    NATIONAL    ELECTRICAL    CODE. 

the  same  way  as  if  we  were  to  say  of  water,  that  a  cur- 
rent of  10  gallons  per  minute  was  flowing  through  a 
pipe. 

Electro-Motive  Force — Pressure  or  Potential. — These 
terms  are  all  used  in  the  code  to  express  the  same 
thing.  We  will  use  the  more  common  term  of  "elec- 
tro-motive force,"  which  is  commonly  abbreviated  to 
E.  M.  F.  E.  M.  F.  may  be  defined  as  a  force  which 
causes,  or  tends  to  cause,  a  current  of  electricity  to 
flow.  To  use  our  same  analogy,  suppose  we  have  a 
tank  full  of  water;  we  shall  have  upon  the  bottom  of  a 
tank  a  pressure  due  to  the  head.  If  we  bore  a  hole 
into  the  bottom  of  the  tank,  we  shall  immediately  have 
a  flow  of  water.  If  we  place  our  hand  over  the  hole, 
the  pressure  will  still  tend  to  cause  a  flow  and  the  flow 
will  be  instantaneous  as  soon  as  the  obstacle  is  removed. 
In  electricity  we  measure  the  pressure  by  an  arbitrary 
unit  called  a  "  volt."  This  corresponds  with  the  pounds 
of  pressure  to  the  square  inch  with  water.  With  water, 
the  greater  the  pressure  the  greater  will  be  the  flow,  the 
outlet  remaining  the  same;  so  with  electricity.  The 
greater  the  E.  M.  F.,  the  greater  will  be  the  current, 
provided  other  conditions  remain  unchanged.  In  fact, 
with  electricity,  the  relation  of  flow  to  pressure  is  more 
simple  than  with  water,  for,  other  things  remaining  the 
same,  if  we  double  our  pressure,  we  double  our  current, 
/.  e.,  the  current  will  be  exactly  proportional  to  the 
pressure;  or  the  amperes  will  be  proportional  to  the 
volts. 

Dynamo. — A  dynamo  is  a  machine  which,  when 
driven  by  an  engine  or  other  source  of  power,  trans- 


DEFINITIONS    OF    COM 

forms  the  work  of  the  engine  or  prime  mover  into  elec- 
tricity. It  may  be  compared  to  a  pump  driven  by  a 
belt.  When  motion  is  transmitted  to  the  pump,  it  sets 
up  a  pressure  which  will  cause,  or  tend  to  cause,  a  flow 
of  water.  So,  when  a  dynamo  is  set  in  motion  by  any 
mechanical  means,  an  electrical  pressure  will  be  set  up, 
and  this  is  called  the  "pressure  "or  "  E.  M.  F."  of  the 
machine.  This  pressure  will  tend  to  cause  a  flow  of 
electricity,  or  an  electrical  current. 

A  dynamo  is  a  reversible  machine,  /.  e.,  it  can  be 
used  to  generate  a  current  of  electricity,  or,  if  the  cur- 
rent of  electricity  is  produced  by  another  source,  and 
sent  through  it,  its  armature  or  moving  part  will  be  set 
in  rotation  and  it  can  be  used  as  a  source  of  power  to 
drive  other  machines.  When  thus  used  it  is  called  a 
"motor."  The  distinction  between  a  dynamo  and  a 
motor  is  one  of  application,  and  not  necessarily  of  con- 
struction. To  make  the  distinction  clear,  it  is  now 
common  to  speak  of  a  machine  which  generates  elec- 
tricity as  a  "generator,"  and  of  one  which  transforms 
electricity  into  mechanical  work  as  a  "motor."  The 
words  "dynamo"  and  "generator"  are  used  in  the 
code  to  mean  the  same  thing. 

Conductor. — Unlike  water,  electricity  does  not  flow 
most  readily  when  not  impeded  by  a  solid  substance. 
In  fact,  while  no  ordinary  pressure  will  cause  electricity 
to  pass  through  the  air,  a  small  pressure  may  cause  an 
immense  current  to  flow  through  a  mass  of  metal.  We 
therefore  say  that  metal  is  a  conductor  of  electricity, 
and  that  air  is  a  non-conductor. 

When  we  wish  to  direct  a  current  of  water  from  one 


1 6  THE    NATIONAL    ELECTRICAL    CODE. 

point  to  another,  we  provide  a  path  free  from  solid 
obstruction  and  we  confine  the  water  through  this  path 
by  some  solid  substance,  such  as  the  bank  of  a  canal 
or  a  metal  pipe.  With  electricity,  however,  we  provide 
a  metallic  path,  such  as  a  copper  wire,  and  the  elec- 
tricity is  kept  from  leaving  the  wire  by  the  surrounding 
air,  or  some  other  non-conducting  material  which  sep- 
arates the  wire  or  metal  path  from  other  paths  into 
which  it  might  flow  if  there  was  no  such  barrier. 

Resistance. — Although  electricity  will  readily  flow  in 
a  metal  wire,  a  given  pressure  will  not  produce  the  same 
flow  in  wires  of  different  metals,  or  in  different  sized 
wires  of  the  same  metal.  Just  as  with  water,  a  given 
pressure  will  not  send  the  same  amount  through  a  small 
hole  as  through  a  large  one,  or  through  a  long  pipe  of 
small  diameter,  as  through  a  short  one  of  large  diame- 
ter, so  a  given  E.  M.  F.  will  send  a  small  current  through 
a  long,  thin  wire,  and  a  strong  current  through  a  short 
and  thick  one.  We  explain  the  different  results  by 
saying  that  the  long,  thin  wire  offers  a  "resistance"  to 
the  flow  of  the  current.  This  we  call  "  electrical  resist- 
ance," or  simply  "resistance."  Resistance  is  measured 
in  "ohms,"  an  ohm  being  an  arbitrary  unit. 

Electrical  resistance  may  be  compared  to  friction  in 
a  pipe  carrying  a  current  of  water ;  the  greater  the 
pressure,  and  the  less  the  friction,  the  greater  will  be 
the  flow.  So,  in  electricity,  the  greater  the  E.  M.  F., 
and  the  less  the  resistance  in  the  path  or  conductor,  the 
greater  will  be  the  current.  Or,  to  express  the  same 
thing  in  electrical  terms,  the  greater  the  voltage  of  our 
dynamo,  and  the  less  the  resistance  of  our  conductor 


DEFINITIONS    OF    COMMON    TERMS.  l^ 

in  ohms,  the  greater  will  be  the  current  in  amperes 
which  will  flow  through  the  conductor. 

Insulator. — If  we  are  to  confine  electricity  to  cur 
"conductor,"  we  must  separate  it  from  other  conduct- 
ors ;  or,  as  we  say,  we  must  "insulate"  it.  This  is 
accomplished  by  surrounding  our  conductor  with  a 
non-conducting  substance,  or  by  supporting  it  by  a 
non-conducting  substance  in  the  air,  which  is  itself  a 
non-conductor.  Any  such  non-conducting  material 
used  to  support  or  surround  a  wire  is  called  an  insu- 
lator. In  practice  it  is  customary  to  speak  of  a  non- 
conducting support  as  an  "  insulator,"  and  of  a  non- 
conducting material  surrounding  a  conductor  or  wire  as 
"insulation."  It  is  evident  that  the  distinction  between 
"insulators"  and  "conductors"  is  simply  relative.  A 
non-conducting  or  insulating  substance  is  simply  a  sub- 
stance of  very  high  resistance,  but  the  resistance  of 
materials  used  for  insulation  are  so  enormous,  that  we 
are  justified  in  calling  them  "non-conductors."  Of  all 
insulators,  dry  air  is  the  best,  and  dry  glass  the  next 
best;  rubber,  porcelain,  oil,  shellac,  mica,  paper,  cot- 
ton, silk,  etc.,  are  the  substances  most  commonly  used. 
As  safety  in  electrical  work  depends  solely  upon  the 
confining  of  the  current  to  its  proper  circuit,  the  prob- 
lem of  safety  is  very  largely  one  of  insulation,  and  it 
will  be  seen  that  the  greater  part  of  the  "code"  is 
devoted  to  specifying  material  and  methods  which  will 
secure  good  insulation. 

Polarity. — The  flow  of  current  from  a  dynamo  is  not 
exactly  analogous  to  the  flow  of  water  from  a  tank, 
since  to  have  a  continuous  current  of  electricity,  we  must 


l8  THE    NATIONAL    ELECTRICAL    CODE. 

have  a  continuous  conducting  circuit;  i.  e.,  the  current 
must  tovt  from  the  dynamo  through  the  circuit  and  back 
again  to  the  dynamo.  In  this  respect  the  dynamo  is 
more  like  our  pump.  We  must  continually  supply 
water  to  the  pump  in  order  to  have  a  continuous  flow. 
Any  electrical  circuit  must  be  continuous  in  order  to 
have  a  current,  and  we  may,  if  we  like,  imagine  the 
condition  similar  to  that  of  water  flowing  round  and 
round  in  an  endless  pipe.  We  assume  that  any  ordinary 
current  flows  always  in  the  same  direction,  and  that  the 
current  from  a  dynamo  goes  out  from  the  machine  on 
one  conductor,  and  back  to  the  machine  on  another. 
We  express  this  by  saying  that  these  two  conductors 
are  of  "opposite  polarity  "  and  the  points  where  they 
join  the  dynamo  we  designate  as  the  two  "poles"  of 
the  machine.  The  pole  where  the  current  emerges  is 
called  the  "positive"  pole,  and  the  one  to  which  it 
returns  is  called  the  "  negative  "  pole.  "  Polarity  "  is 
naturally  relative,  and  we  speak  of  any  part  of  a  circuit 
as  being  positive  with  reference  to  another,  when  the 
current  flows  from  the  first  point  to  the  second,  or  when 
the  pressure  tends  to  set  up  such  a  current.  Other 
electrical  terms  which  appear  in  the  "code "will  be 
defined  as  we  come  to  them. 


CHAPTER    II. 

CENTRAL    STATIONS    FOR    LIGHT    AND    POWLR.        PART    I. 

TEXT  OF  CODE  ON  CENTRAL  STATIONS.  CLASS  A.  (These 
Rules  also  apply  to  dynamo  rooms  in  isolated  plants,  connected 
with  or  detached  from  buildings  used  for  other  purposes;  also  to 
all  varieties  of  apparatus  therein  of  both  high  and  low  potential.) 

1.  GENERATORS: — a.   Must  be  located  in  a  dry  place,    b.   Must 
be  insulated  on  floors  or  base  frames,  which  must  be  kept  filled, 
to  prevent  absorption  of  moisture,  and  also  kept  clean  and  dry. 
c.    Must  never  be  placed  in  a  room  where  any  hazardous  process 
is  carried  on,  nor  in  places  where  they  would  be  exposed  to  inflam- 
mable gases,  or  flyings,  or  combustible  material,     d.    Must  each 
be  provided  with  a  waterproof  covering. 

2.  CARE  AND  ATTENDANCE: — A  competent  man  must  be  kept 
on  duty  in  the  room  where  generators  are  operating.      Oily  waste 
must  be  kept  in  approved  metal  cans,  and  removed  daily. 

3.  CONDUCTORS: — From  generators,  switch  boards,  rheostats 
or  other  instruments,  and  thence  to  outside  lines,  conductors — a. 
Must  be  in  plain  sight  and  readily  accessible,     b.    Must  be  wholly 
on  non-combustible  insulators,  such  as  glass  or  porcelain,    c.   Must 
be  separated  from  contact  with  floors,  partitions  or  walls  through 
which  they  may  pass,  by  non-combustible  insulating  tubes,  such 
as  glass  or  porcelain,     d.    Must  be  kept  rigidly  so  far  apart  that 
they  cannot  come  in  contact,     e.    Must  be   covered  with  non- 
inflammable  insulating  material  sufficient  to  prevent  accidental 
contact,  except  that  "bus  bars"  may   be  made  of  bare  metal. 
f.    Must  have  ample  carrying  capacity,  to  prevent  heating. 

The  name  "Central  Station"  is  applied  to  any  elec- 
trical  plant   from   which    electricity   is   furnished    for 

(19) 


20  THE    NATIONAL    ELECTRICAL    CODE. 

operating  street  lights  or  for  supplying  electricity  for 
lamps  or  motors,  in  a  similar  manner  to  that  in  which 
a  gas  company  furnishes  gas  for  heat  and  light.  By  an 
"  Isolated  Plant  "  is  meant  an  electrical  plant  for  light- 
ing a  single  building  or  a  number  of  buildings  owned 
by  one  person  or  company.  The  distinction  is  not 
arbitrary,  and  it  will  be  noted  that  the  code  lays  down 
the  same  rules  for  the  installation  of  machinery  and 
apparatus  in  the  dynamo  room  of  an  isolated  plant  as 
in  a  building  devoted  exclusively  to  an  electric  plant. 
So  we  will  not  try  to  give  any  more  precise  definition 
than  the  above.  A  Central  Station  has  extra  hazards 
due  to  its  outside  lines  on  poles  or  underground,  which 
may  accidentally  come  into  contact  with  the  ground, 
with  one  another  or  with  the  wires  of  other  systems;  or 
may,  if  improperly  installed,  conduct  lightning  into  the 
station.  In  installing  an  isolated  plant,  on  the  other 
hand,  equal  care  is  necessary,  as  any  hazard  to  the 
plant  endangers  the  building  in  which  it  is  located,  and 
also  the  contents  of  the  building. 

Before  discussing  electrical  construction,  let  us  con- 
sider how  it  is  that  an  electrical  current  can  cause  a 
hazard.  If  a  current  flows  in  a  wire,  we  have  found 
that  its  flow  is  opposed  by  something  analogous  to  fric- 
tion, which  we  have  called  resistance.  The  energy 
required  to  overcome  this  resistance  is  transformed  into 
heat  just  as  mechanical  work  expended  to  overcome 
friction  is  transformed  into  heat.  The  greater  the  cur- 
rent and  the  greater  the  resistance,  the  more  energy  will 
be  absorbed  in  heating  our  wire.  With  a  current  of 
sufficient  strength,  we  can  heat  any  wire  red  hot,  or, 


CENTRAL    STATIONS.  21 

for  that  matter,  we  can  melt  it.  If,  therefore,  our  con- 
ductors are  so  installed  that  an  accident  may  load  them 
with  an  excessive  current,  we  may  have  enough  heat 
generated  to  char  their  insulation,  or  even  to  set  fire  to 
the  insulation  or  any  adjacent  combustible  material. 
We  can  prevent  undue  heating  by  using  wires  of  proper 
size  for  the  required  current,  and  protecting  them  from 
a  greater  current  by  safety  devices  (described  later); 
and  we  can  secure  additional  safety  by  installing  the 
wires  in  such  a  manner  that  even  if  they  do  become 
excessively  hot,  the  heat  will  not  be  conducted  to  com- 
bustible material.  Again,  if  we  have  a  wire  carrying  a 
small  current  from  a  dynamo,  and  if  we  open  the  cir- 
cuit, for  example  by  cutting  the  wire,  we  will,  upon 
separating  the  two  ends,  have  a  flash  or  "  spark,"  as  it 
is  called.  This  spark  gives  out  but  little  heat,  but  it 
will  ignite  an  explosive  mixture;  we  are  all  familiar 
with  its  use  in  electric  gas  lighting.  If,  however,  the 
current  be  one  of  several  amperes,  when  we  separate 
the  ends  of  our  wires  for  a  short  distance,  the  current 
will  flow  across  the  gap.  This  is  called  an  "electric 
arc."  It  is  a  flame,  and  its  heat  is  so  intense  that  it 
will  melt  steel  like  wax  in  the  flame  of  a  candle.  It  is 
this  arc  that  gives  the  light  in  an  "  arc  "  lamp,  and  this 
is  the  thing  we  may  get  in  a  system  of  conductors  when 
wires  of  opposite  polarity  come  in  contact  with  one 
another,  or  when  any  accident  breaks  a  wire  carrying  a 
large  current.  The  current  required  for  six  or  eight 
ordinary  incandescent  lamps  will  maintain  an  arc  equal 
to  that  of  a  small  arc  lamp. 

The  accidental  forming  of  an  arc  may  be  prevented 


22  THE    NATIONAL    ELECTRICAL    CODE. 

by  proper  insulation  and  workmanship.  Fortunately, 
we  can,  by  proper  workmanship  and  material  and  the 
use  of  simple  devices,  install  our  conductors  so  that  we 
can  obtain  light  and  power  with  less  hazard  from  elec- 
tricity than  from  any  other  source.  Poor  insulation  of 
conductors  causes  trouble  by  allowing  the  current  to 
leave  the  conductor  and  flow  through  some  other  path. 
This  improper  path,  like  any  other,  must  be  continuous, 
i.  e.,  the  current  will  not  leak  from  the  wire  to  a  con- 
ducting substance  in  contact  with  it  unless  there  is 
another  contact  where  it  can  return  to  the  circuit. 
Two  contacts  to  a  conducting  substance  are  necessary 
to  set  up  a  leak.  The  substance  may  be  some  metal  or 
any  substance  which  can  absorb  moisture.  Although 
pure  water  is  a  poor  conductor,  water  which  is  dirty  or 
which  contains  any  salt  or  acid,  in  solution,  is  a  good 
conductor.  Most  of  the  non-metallic  material  used  in 
building  construction  is  non-conducting  when  dry,  but 
will  conduct  the  current  readily  when  wet.  The  enemy 
of  insulation  is  moisture. 

Generators. — A  dry  location  is  especially  necessary 
for  a  generator.  If  moisture  condenses  upon  the 
dynamo  while  it  is  not  running,  it  may  destroy  the 
insulation  of  the  wire  with  which  it  is  wound.  If  the 
wire  is  simply  covered  with  a  thin  covering  of  cotton, 
as  is  the  usual  practice,  leaks  may  be  set  up  between 
the  different  wires,  resulting  finally  in  the  burning  of 
the  insulation;  or  the  insulation  between  the  earth  and 
the  conductors  on  the  machine  may  be  destroyed,  thus 
endangering  both  dynamo  and  circuits.  Further,  where 
machines  of  very  high  E.  M.  F.  are  used,  a  damp  floor 


CENTRAL    STATIONS.  23 

or  poorly  insulated  machine  may  endanger  the  life  of 
the  attendant,  or  at  least  discourage  him  from  properly 
attending  to  the  machine. 

As  the  current  always  flows  in  a  closed  circuit,  we 
must  have  two  "faults"  in  our  insulation  in  order  to 
have  a  leak.  When  we  have  one  fault,  the  second  may 
come  at  any  instant,  and  the  first  fault  may  set  up  a 
strain  upon  a  weak  point  in  the  insulation  and  help  to 
develop  a  second  one.  The  most  common  cause  of 
leakage  in  a  Central  Station  system  is  formed  by  the 
conductor  of  a  circuit  coming  in  contact  with  the  earth. 
This  contact  is  called  a  "ground."  It  is  common 
usage  to  speak  of  the  contact  of  a  wire  with  any  con- 
ducting substance  as  a  "  ground,"  and  when  we  have 
such  a  contact,  we  say  that  the  Wire  is  grounded  upon 
the  substance.  For  example,  if  a  wire  touched  a  gas 
pipe  it  would  be  grounded,  and  we  would  speak  of  it  as 
being  grounded  on  the  pipe,  even  if  the  pipe  were  not 
connected  to  the  earth. 

The  mounting  of  a  dynamo  upon  an  insulating  base 
or  frame  as  required  by  the  code  is  desirable  in  a  light- 
ing plant,  as  an  extra  precaution.  The  wires  upon  the 
dynamo  are  insulated  from  the  iron  frame  of  the 
machine;  but,  as  this  insulation  may  be  injured  by  an 
over-load,  by  lightning  or  by  mechanical  injury,  the 
further  precaution  is  taken  of  insulating  the  frame  from 
the  earth,  as  a  leak  from  dynamo  to  earth  may  be  more 
serious  than  one  upon  a  circuit,  as  its  extent  is  not  lim- 
ited by  safety  devices.  The  observance  of  rule  "c" 
concerning  generators  is  important.  An  arc  may  be 
formed  by  the  breaking  of  a  wire,  or  by  the  intentional 


24  THE    NATIONAL    ELECTRICAL    CODE. 

opening  of  a  circuit  carrying  current.  It  is  impossible 
to  guard  against  a  spark  in  a  dynamo  room.  The  cur- 
rent in  a  dynamo  is  generated  in  the  moving  part  or 
armature,  and  it  is  led  to  the  circuit  through  an  attach- 
ment to  the  armature  called  a  "  commutator  "  or  "col- 
lector" (according  to  its  design),  the  conductors  of  the 
circuit  being  electrically  connected  to  the  commutator 
or  collector  by  stationary  strips  of  copper  or  blocks  of 
carbon  called  ' '  brushe s. "  Any  defect  in  design  or 
workmanship,  improper  adjustment,  overloading  of  the 
machine,  or  even  the  presence  of  dust,  may  at  any  time 
cause  "sparking"  at  the  brushes.  The  cover  specified 
in  rule  "  d  "  is  to  protect  the  machine  while  not  in  ser- 
vice from  dirt  and  moisture,  as  from  leaky  pipes, 
defective  roofs,  etc.  It  may  also  prove  useful  to  pre- 
vent damage  by  water  in  the  extinguishing  of  an  incip- 
ient fire. 

Care  and  Attendance. — As  a  variety  of  accidents  may 
cause  a  dynamo  to  spark  so  badly  as  to  throw  off  sparks 
to  a  considerable  distance,  or  may  even  cause  the 
"  burning  out  "  of  an  armature,  it  needs  no  argument 
to  show  that  an  attendant  ought  always  to  be  near. 
Any  serious  trouble  on  the  circuit  will  usually  be  indi- 
cated in  some  manner  in  the  dynamo  room,  and  prompt 
inspection  may  discover  a  hazard  in  time  to  remove  it 
without  loss.  The  rule  about  oily  waste  should,  of 
course,  apply  wherever  waste  is  used.  Its  habit  of 
indulging  in  spontaneous  combustion,  especially  when 
it  has  a  good  chance  to  set  fire  to  something  else,  is  too 
well  known  to  insurance  men  to  call  for  comment. 

Conductors. — Originally   it  was   customary   to   place 


CENTRAL    STATIONS.  25 

electrical  instruments  and  regulating  and  controlling 
devices  either  directly  upon  the  wall  of  the  dynamo 
room  or,  at  best,  to  mount  them  upon  a  wooden  board 
fastened  to  the  wall.  The  board  was  called  a  "  switch 
board."  This  name  is  now  applied  to  any  structure 
carrying  instruments  and  regulating  and  controlling 
devices.  In  a  dynamo  room  or  station,  all  circuits 
from  the  dynamos  are  led  to  a  main  switch  board,  and 
thence  the  cunent  is  distributed  by  the  necessary  cir- 
cuits to  the  lamps  or  motors.  The  switch  board  con- 
trols the  entire  output  of  the  plant,  and  often  carries 
many  regulating  and  controlling  devices  and  a  large 
amount  of  complicated  wiring.  Many  of  the  fires  in 
the  poorly  constructed  stations  of  the  past  have  origi- 
nated in  the  switch  boards  or  their  vicinity.  It  would 
seem  evident  that  the  wires  to  and  from  the  switch 
board  should  be  in  sight  and  accessible;  yet,  in  many 
plants,  wires  have  been  run  from  dynamo  to  switch 
board  under  wooden  floors,  and  all  the  wires  to  and 
from  the  switch  board  have  been  crowded  between  the 
board  and  the  wall  in  an  inaccessible  space.  This  has 
been  done  for  appearance  sake,  it  being  easier  for  the 
constructor  to  conceal  poor  work  than  to  do  work  in  a 
mechanical  and  workmanlike  manner.  The  unfortunate 
experience  of  insurance  companies  with  central  stations 
has  been  largely  due  to  this  kind  of  engineering.  Rules 
"  b  "  and  "  c  "  describe  the  safest  possible  kind  of  con- 
struction; i.  <?.,  such  that  current  cannot  leak  from  the 
wires  even  if  their  insulating  covering  is  defective,  and 
even  if  the  wires  become  overheated,  the  heat  cannot 
be  communicated  to  any  combustible  material.  With 


26  THE    NATIONAL    ELECTRICAL    CODE. 

such  construction,  a  bare,  red-hot  wire  would  not  set  a 
fire. 

As  regards  rule  "d,"  no  other  rule  for  distances 
between  wires  can  be  laid  down,  but  safe  work  can  be 
done  by  having  numerous  insulating  supports  of  proper 
design.  We  might  add  to  the  rule  by  saying:  "Keep 
the  conductors  of  opposite  polarity  as  far  apart  as  space 
and  circumstances  will  permit."  With  conductors  run 
upon  glass  or  porcelain,  it  is  more  important  to  have 
the  covering  of  the  wire  fire  proof  than  moisture  proof. 
Rule  "e"is  usually  interpreted  to  mean  that  a  high 
grade  of  insulated  wire  should  be  used,  and  that  the 
insulation  should  have  a  flame-proof  covering  or  braid. 
The  best  practice  for  a  dry  station  is  to  use  a  fire-proof 
covering  and  to  depend  upon  porcelain  and  glass  for 
insulation  in  case  of  accidental  dampness.  It  should 
be  the  engineer's  aim  to  secure  good  insulation  in  any 
event,  and  to  do  it  with  the  smallest  possible  amount 
of  combustible  material.  In  many  cases,  this  means 
none  at  all.  Where  several  dynamos  are  run  in  a  power 
or  incandescent  lighting  plant,  it  is  common  practice  to 
lead  all  the  circuits  from  the  dynamos  to  one  pair  or 
set  of  conductors  upon  the  switch  board,  and  from 
these  conductors  to  lead  off  all  the  lighting  or  power 
circuits.  These  main  conductors  are  usually  so  large 
that  flat  copper  bars  are  used  instead  of  wires.  These 
bars,  as  they  carry  the  entire  load  of  the  plant,  are 
called  "bus  bars."  The  bus  bars  are  usually  bolted 
fast  in  position,  and,  as  there  is  no  possibility  of  their 
getting  out  of  place,  it  is  perfectly  safe  to  have  them 
insulated  only  by  their  supports.  The  rule  "  g,"  con- 


CENTRAL    STATIONS.  27 

earning  "carrying  capacity,"  simply  means  that  the 
wires  must  be  large  enough  so  that  they  will  not  heat 
unduly  with  any  current  that  they  may  ever  be  called 
upon  to  carry.  This  subject  is  taken  up  more  fully  in 
another  portion  of  the  code. 


CHAPTER    III. 

CENTRAL    STATIONS    FOR    LIGHT    AND    POWER.       PART    II. 

TEXT  OF  CODE  COVERED  BY  THIS  CHAPTER.  4.  SWITCH 
BOARDS: — Should  be  approved  before  being  placed,  a.  Must  be 
so  placed  as  to  reduce  to  a  minimum  the  danger  of  communicating 
fire  to  adjacent  combustible  material,  b.  Must  be  accessible 
from  all  sides  when  the  connections  are  on  the  back;  or  may  be 
placed  against  a  brick  or  stone  wall  when  the  wiring  is  entirely  on 
the  face.  c.  Must  be  kept  free  from  moisture,  d.  Must  be  made 
of  non-combustible  material,  or  of  hardwood  in  skeleton  form, 
filled  to  prevent  absorption  of  moisture,  e.  Bus  bars  must  be 
equipped  in  accordance  with  Rule  3  for  placing  conductors. 

5.  RESISTANCE  BOXES  AND  EQUALIZERS:  — a.  Must  be  equipped 
with  metal  or  non-combustible  frames,     b.  Must  be  placed  on  the 
switch  board,  or,  if  not  thereon,  at  a  distance  of  a  foot  from  com- 
bustible material,  or  separated  therefrom  by  a  non-inflammable, 
non-absorptive,  insulating  material. 

6.  LIGHTNING  ARRESTERS: — a.   Must  be  attached  to  each  side 
of  every  over-head  circuit  connected  with  the  station,     b.   Must 
be  mounted  on  non-combustible  bases  in  plain  sight  on  the  switch 
board,  or  in  an  equally  accessible  place,  away  from  combustible 
material,     c.   Must  be  connected  with  at  least  two  "  earths  "  by 
separate  wires,  not  smaller  than  No.  6  B.  &  S  ,  which  must  not 
be  connected  to  any  pipe  within  the  building,     d.   Must  be  so 
constructed  as  not  to  maintain  an  arc  after  the  discharge  has 
passed. 

Switchboards. — Rule  "a  "covers  in  a  general  way 
the  question  of  location,  and  common  sense  should 
enable  any  constructor  to  apply  the  rule  in  a  particular 

(28) 


CENTRAL    STATIONS.  29 

case.  The  front  of  a  switch  board  usually  carries  a 
number  of  instruments,  switches  and  safety  devices,  so 
that  in  most  cases  it  is  desirable  to  place  our  conduct- 
ors upon  the  back  of  the  board.  In  a  large  plant  there 
are  usually  a  great  many  instruments  and  appliances, 
and  as  the  dimensions  of  the  switch  board  are  limited 
both  by  the  amount  of  space  available  and  by  the 
requirements  of  convenient  operation,  it  is  almost  abso- 
lutely necessary  to  place  the  conductors  behind  the 
board.  Originally,  wires  were  placed  behind  the  board 
so  that  rough  and  cheap  work  could  be  done.  The 
work  upon  the  back  of  a  switch  board  should  be  as  neat 
and  mechanical  as  that  upon  the  front,  and  this  is  a 
good  test  of  the  ability  and  the  intent  of  the  installing 
engineer. 

"Accessible  "  in  rule  "  b  "  should  mean  not  only  that 
the  conductors  must  be  readily  accessible  for  inspec- 
tion, but  also  that  there  must  be  ample  room  behind 
the  switch  board  for  a  man  to  work  and  to  do  good 
work.  This  is  essential,  as  it  is  often  necessary  for  a 
man  to  work  behind  a  board  while  the  conductors  are 
carrying  current,  or,  as  it  is  commonly  expressed,  while 
the  board  is  carrying  "live"  circuits.  When  a  board 
is  placed  against  a  brick  wall,  all  wiring  should  of 
course  be  upon  the  face  of  the  board,  and  it  should  not 
be  allowable  to  attach  conductors  of  any  kind  to  the 
board  by  metal  screws  or  bolts  extending  through  the 
board. 

Two  kinds  of  switch  board  construction  are  allowa- 
ble by  the  code.  We  may  make  our  board  entirely  of 
slabs  of  slate  or  marble  fastened  to  metal  supports;  or 


30  THE    NATIONAL    ELECTRICAL    CODE. 

we  may  erect  a  wooden  framing  attaching  to  the  front 
our  instruments,  switches  and  controlling  devices,  each 
appliance  having  its  slate  or  marble  base,  and  the  con- 
ductors being  supported  on  the  back  of  the  frame  upon 
glass  or  porcelain  insulators.  Frame  or  " skeleton" 
construction  may  be  made  safe,  but  it  requires  more 
care  and  skill  to  do  a  neat-looking  job  of  wiring  upon  a 
skeleton  board  than  upon  one  of  slate  or  marble,  and 
the  slate  or  marble  board  costs  but  little  more  than  the 
bases  which  are  required  when  a  "skeleton"  board  is 
used.  The  superior  appearance  of  a  marble  board 
usually  justifies  the  slight  additional  expense.  Marble 
is  better  than  slate  as  an  insulator,  and  but  slightly 
more  expensive.  The  purer  the  marble,  the  better; 
and  where  the  switch  board  carries  currents  of  very 
high  pressures,  the  marble  should  be  carefully  selected, 
and  should  be  free  from  any  impurities  that  might 
impair  its  insulating  qualities. 

Resistance  Boxes  and  Equalizers. — A  Resistance  Box 
or  Rheostat  is  a  regulating  device  introduced  into  an 
electric  circuit  for  the  purpose  of  reducing  the  current 
or  the  electro-motive  force.  It  is  simply,  as  its  name 
indicates,  a  resistance.  The  earliest  form  in  common 
use  consisted  of  coils  of  wire  of  a  poorly  conducting 
material,  such  as  iron  or  German  silver.  These  coils 
were  mounted  in  a  box,  and  the  top  of  the  box  carried 
a  switch,  by  means  of  which  more  or  fewer  coils  could 
be  introduced  into  the  circuit,  so  that  by  turning  a 
handle  or  wheel  the  resistance  of  a  circuit  could  be 
varied.  When  we  add  resistance  to  a  circuit,  the 
E.  M.  F.  or  pressure  which  tends  to  send  a  current 


CENTRAL    STATIONS.  3! 

through  our  lamps  or  motors  is  decreased,  and  if  the 
rest  of  our  circuit  remains  unchanged,  the  current  will 
also  be  proportionately  decreased.  A  rheostat  corre- 
sponds to  the  throttle  on  a  steam  engine.  When  a  rhe- 
ostat is  used  for  controlling  a  current  in  the  magnet  or 
"field"  circuit  of  a  dynamo,  it  is  called  a  "Dynamo 
Rheostat"  or  "Field  Regulator,"  or  simply  a  "Resist- 
ance Box."  When  it  is  placed  in  the  circuit  of  a  motor 
it  is  called  a  "Starting  Box  "  or  "Rheostat."  When 
rheostats  are  used  to  reduce  the  pressure  upon  a  num- 
ber of  circuits  having  a  common  starting  point,  they 
are  called  "Equalizers."  Where  a  rheostat  is  used  in 
theatrical  work  for  "turning  down  the  lights,"  it  is 
called  a  Dimmer.  The  most  general  term  is  "Rheo- 
stat," which  applies  to  any  resistance  that  can  be  varied 
at  will. 

The  regulating  of  a  current  by  inserting  resistance 
always  means  a  loss  of  energy.  This  energy  is  trans- 
formed into  heat  in  the  rheostat.  In  order  to  make  a 
rheostat  small  enough  to  be  used  in  commercial  work, 
it  is  necessary  to  allow  the  wires  to  get  pretty  hot.  It 
is  therefore  evident  that  rheostats  should  be  carefully 
designed  and  installed.  Perhaps  the  worst  points  of 
danger  in  many  of  the  central  stations  of  the  past  were 
in  the  Equalizer,  made  of  coils  of  iron  wire  in  wooden 
boxes.  Rheostats  may  be  made  perfectly  safe  by  mak- 
ing them  wholly  of  non-inflammable  material,  and 
excluding  all  inflammable  material  from  their  vicinity. 
They  are  sources  of  heat,  and  should  be  treated  as 
"  stoves." 

Lightning  Arresters. — A  lightning  arrester  is  not  a 


32  THE    NATIONAL    ELECTRICAL    CODE. 

device  to  arrest  lightning,  although  that  is  "what  that 
name  might  imply."  Lightning,  when  once  it  gets 
upon  our  wires,  is  always  looking  for  a  chance  to  get 
to  earth,  and  a  lightning  arrester  is  a  device  intended 
to  assist  the  lightning  to  get  to  the  earth  by  an  easy 
path,  and  thus  prevent  it  from  taking  a  path  where  it 
might  cause  fire  or  other  damage.  A  lightning  dis- 
charge has  a  sufficiently  high  electrical  pressure  to 
overcome  the  insulation  of  our  wire.  In  fact,  it  will 
get  to  ground  somewhere,  even  if  it  has  to  jump  a  con- 
siderable distance  to  the  earth.  It  will  take  the  easiest 
path.  Without  proper  protection,  this  path  may  be 
through  the  insulation  of  our  dynamo  (especially  if  the 
iron  frame  of  the  dynamo  is  grounded),  or  it  may  be 
from  our  wire  to  a  gas  pipe  in  a  fixture  carrying  both 
gas  and  electric  lights,  or  it  may  be  at  any  weak  point 
in  the  insulation  of  our  conductors  from  the  earth. 

Most  forms  of  lightning  arresters  consist  simply  of  a 
piece  of  conducting  material  brought  close  to  another 
piece  of  conducting  material,  so  that  the  two  are  sepa- 
rated only  by  a  very  small  air  gap.  The  most  simple 
form  consists  of  two  rectangular  plates  of  brass  or  car- 
bon laid  upon  slate  or  marble  so  that  their  edges  nearly 
touch,  one  plate  being  connected  to  our  circuit  which 
is  to  be  protected,  and  the  other  to  the  earth.  The 
adjacent  edges  are  usually  notched,  as  this  assists  the 
discharge.  Although  the  E.  M.  F.  of  our  dynamos  will 
not  cause  a  current  to  pass  across  a  very  small  air  gap, 
the  E.  M.  F.  of  a  lightning  discharge  is  so  high  that  the 
gap  offers  no  apparent  resistance  to  its  passage.  Such 
is  the  nature  of  electricity  in  this  form  that  it  may  jump 


CENTRAL    STATIONS.  33 

an  air  gap  of  considerable  width,  rather  than  pierce  a 
comparatively  poor  insulation  at  another  point  not  far 
away  upon  the  same  circuit. 

The  great  danger  from  lightning  is  that  it  destroys 
our  insulation.  We  have  seen  that  although  the  pres- 
sure of  an  ordinary  dynamo  will  not  cause  a  current  to 
pass  over  a  very  minute  air  gap,  still  when  we  touch 
two  wires  of  opposite  polarity  together  and  then  sepa- 
rate them  the  same  pressure  will  permanently  maintain 
an  arc  of  considerable  length.  So  when  lightning 
passes  to  ground  across  an  air  gap  it  may  start  an  arc 
which  will  be  maintained  by  our  dynamo  with  disastrous 
results.  The  entire  theory  of  lightning  arresters  is  too 
long  to  discuss  in  this  volume,  but  the  principles  of 
protection  from  lightning  are  pretty  well  understood, 
and  except  in  certain  localities  we  can  secure  ample 
protection  by  using  any  one  of  a  number  of  com- 
mercial forms  of  lightning  arrester,  provided  we  use 
enough  of  them  and  have  them  well  distributed  over 
our  system  of  over-head  conductors. 

Lightning  arresters  are  of  course  not  needed  in  an 
isolated  plant  not  having  out-door  conductors.  Rule 
"a"  calls  for  an  arrester  on  each  side  of  every  circuit. 
This  is  necessary,  for  if  arresters  were  placed  only  upon 
one  side  (that  is  attached  to'  only  one  pole  of  our 
circuit)  the  lightning  would  have  to  go  through  our 
dynamo  or  our  lamps  or  motors  before  it  could  get 
from  the  other  pole  to  an  arrester. 

As  regards  Rule  "b,"  everyone  knows  that  lightning 
moves  in  mysterious  ways,  that  while  its  action  lasts 
but  an  instant  it  may  leave  destruction  in  its  path;  and 

3 


34  THE    NATIONAL    ELECTRICAL    CODE. 

when  we  consider  that  our  dynamo  may  send  a  destruc- 
tive arc  to  follow  up  the  lightning,  it  is  apparent  that 
arresters  should  always  be  separated  and  as  far  as  pos- 
sible removed  from  combustible  material,  and  should 
be  placed  where  they  can  be  readily  inspected  and 
repaired  when  injured  by  a  discharge,  as  often  hap- 
pens. It  is  the  judgment  of  experts  who  have  most 
thoroughly  investigated  lightning  discharges,  as  well  as 
of  engineers  who  have  observed  the  effects  of  lightning, 
that  it  is  better  to  steer  the  lightning  to  earth  outside  of 
the  station  than  to  invite  it  inside  and  then  attempt  to 
direct  its  movements.  Whether  we  have  lightning 
arresters  on  our  switch  board  or  not,  we  should  have 
them  on  our  overhead  line,  and  if  we  can  get  arresters 
that  will  work  all  right  on  a  pole,  it  would  seem  that  a 
pole  just  outside  the  station  was  a  better  place  than  a 
switch  board  for  the  arresters  to  protect  our  machines 
and  station. 

Rule  "c  "  requires  lightning  arresters  to  be  connected 
with  ground  by  two  separate  wires,  and  this  is  desirable 
as  it  is  often  very  difficult  to  get  a  good  earth  contact 
(when  you  want  one).  A  good  connection  to  a  grounded 
pipe  in  a  building  might  invite  unknown  trouble,  and  a 
poor  connection  would  be  the  means  of  leading  the 
lightning  into  the  building  without  giving  it  an  adequate 
means  of  escape.  In  case  the  pipe  should  become  dis- 
connected from  the  earth,  its  use  as  an  earth  connec- 
tion would  simply  lead  the  lightning  into  the  building 
and  turn  it  loose  upon  a  network  of  pipes,  leaving  it  to 
make  its  escape  at  its  own  convenience.  This  kind  of 
thing  has  been  done  very  often,  and  if  the  results  have 


CENTRAL    STATIONS.  35 

not  always  been  disastrous,  it  has  only  been  due  to  the 
element  of  chance,  which  seems  to  play  such  a  large 
part  in  the  movements  of  lightning.  Rule  "d"  is 
called  forth  by  the  fact,  as  above  stated,  that  a  dynamo 
will  maintain  an  arc  which  lightning  has  started.  Such 
an  arc  would,  of  course,  destroy  the  lightning  arrester 
even  if  it  did  no  other  damage.  There  are  many 
devices  for  either  breaking  the  arc  thus  formed  or  for 
preventing  an  arc  being  formed,  and  these  devices  con- 
stitute the  only  essential  points  of  difference  between 
lightning  arresters.  The  type  of  lightning  arrester 
which  is  best  adapted  to  any  given  plant  depends  upon 
the  pressure  and  current  of  the  dynamos  and  circuits 
and  the  kind  of  work  to  which  the  current  is  to  be 
applied.  We  need  only  state  here  that  there  are  upon 
the  market  satisfactory  devices  adapted  to  all  condi- 
tions of  practice. 


CHAPTER    IV. 

CENTRAL    STATIONS    FOR    LIGHT    AND    POWER.         PART    III. 

TEXT  OF  CODE  COVERED  BY  THIS  CHAPTER.  7.  TESTING: — 
a.  All  series  and  alternating  circuits  must  be  tested  every  two 
hours  while  in  operation,  to  discover  any  leakage  to  earth,  abnor- 
mal in  view  of  the  potential  and  method  of  operation,  b.  All 
multiple  arc  low  potential  systems  (300  volts  or  less)  must  be  pro- 
vided with  an  indicating  or  detecting  device,  readily  attachable, 
to  afford  easy  means  of  testing  where  the  station  operates  contin- 
uously, c.  Data  obtained  from  all  tests  must  be  preserved,  for 
examination  by  insurance  inspectors. 

These  rules  on  testing  to  be  applied  at  such  places  as  may  be 
designated  by  the  association  having  jurisdiction. 

8.  MOTORS: — a.   Must  be  wired  under   the  same  precautions 
as  with  a  current  of   the  same  volume  and  potential  for  lighting. 
The  motor  and  resistance-box  must  be  protected  by  a  double  pole 
cut-out  and  controlled  by  a  double  pole  switch,  except  in  cases 
where  one-quarter  horse-power  or  less  is  used  on  low  tension  cir- 
cuit a  single  pole  switch  will  be  accepted,    b.  Must  be  thoroughly 
insulated,  mounted  on   filled  dry  wood,  be  raised  at  least  eight 
inches  above  the  surrounding  floor,  be  provided  with  pans  to  pre- 
vent oil  from   soaking  into   the  floor,   and  must  be  kept  clean. 
c.   Must  be  covered  with  a  waterproof  cover  when  not  in  use,  and, 
if  deemed  necessary  by  the  inspector,  be  inclosed  in  an  approved 
case. 

9.  RESISTANCE  BOXES: — a.   Must  be  equipped  with  metal  or 
other  non-combustible  frames,     b.  Must  be  placed  on  the  switch- 
board, or  at  a  distance  of  a  foot  from  combustible  material,  or 
separated  therefrom  by  a  non-inflammable,  non-absorptive,  insu- 
lating material. 

(36) 


CENTRAL    STATIONS.  37 

Testing. — We  have  thus  far  treated  of  methods  of 
securing  good  insulation.  Proper  maintenance  is  just 
as  important  as  proper  installation.  It  is  always  dif- 
ficult to  maintain  the  insulation  upon  the  circuits  of  a 
Central  Station,  especially  where  there  are  many  and 
long  circuits.  We  must  always  remember  that  a  ground 
upon  a  wire  of  one  polarity  puts  a  strain  upon  the  insu- 
lation of  all  the  wires  of  opposite  polarity.  If  a  second 
ground  comes  upon  a  wire  in  a  building,  it  may  cause 
serious  trouble,  even  if  the  first  ground  is  out  in  the 
street.  Rule  "a"  is  not  very  specific,  as  it  simply 
states  that  the  circuit  shall  be  "tested."  This  might 
mean  a  rough  test,  which  would  only  indicate  the 
presence  of  trouble.  The  insulation  of  the  circuits 
should  be  measured  frequently,  and  these  measure- 
ments recorded.  These  measurements  can  be  made 
while  the  circuits  are  in  operation  by  using  a  suitable 
volt  meter,  or  an  instrument  specially  designed  for  that 
purpose. 

Series  Circuit. — If  we  attach  one  end  of  a  wire  to 
one  brush  or  pole  of  a  dynamo  and  the  other  end  to  the 
other  pole,  it  will  form  what  we  call  a  circuit.  If  the 
dynamo  is  in  motion,  a  current  will  flow  through  the 
wire.  The  strength  of  current  will  depend  upon  the 
electrical  pressure  or  E.  M.  F.  between  the  two  poles 
of  the  dynamo,  and  upon  the  resistance  of  the  wire 
(this  resistance  being  determined  by  the  size  and  length 
of  the  wire  and  the  material  of  which  it  is  made).  If 
we  cut  this  wire  at  any  point,  and  bridge  over  the  gap 
thus  formed  by  inserting  therein  a  lamp,  our  current 
will  now  flow  through  the  lamp.  If  we  cut  the  wire  in 


38  THE    NATIONAL    ELECTRICAL    CODE. 

a  second  place  and  insert  there  a  second  lamp,  the  cur- 
rent will  flow  through  both  lamps.  We  describe  such 
an  arrangement  by  saying  that  the  lamps  are  connected 
in  "series."  By  making  more  cuts  and  inserting  a 
lamp  in  each  gap,  we  can  connect  up  any  number  of 
lamps  in  series,  and  as  the  current  always  flows  in  a 
closed  circuit,  the  same  current  will  flow  through  each 
and  all  the  lamps.  This  method  of  connection  is  com- 
monly used  for  arc  lamps.  As  each  lamp  offers  some 
resistance  to  the  flow  of  the  circuit,  we  will  increase 
the  resistance  of  our  total  circuit  or  path  every  time 
that  we  add  a  lamp.  The  increased  resistance  will 
decrease  our  current  unless  at  the  same  time  we  increase 
the  pressure  of  our  dynamo.  For  example,  the  current 
required  to  properly  operate  a  two  thousand  candle 
power  arc  lamp,  such  as  is  commonly  used  in  street 
lighting,  is  10  amperes.  It  requires  a  pressure  of  50 
volts  to  send  this  current  through  one  lamp.  If  now 
we  insert  a  second  lamp  in  series  with  the  first,  it  will 
require  an  additional  50  volts,  or  a  total  pressure  of 
100  volts  to  send  10  amperes  through  both  lamps.  If 
we  insert  10  lamps  in  the  series,  it  will  require  50  volts 
for  each  lamp,  or  a  total  of  500  volts  to  push  10 
amperes  through  the  entire  series.  It  naturally  follows, 
therefore,  that  if  we  wish  to  run  a  great  many  lamps  in 
one  series,  we  must  have  a  very  high  pressure.  The 
code  regards  anything  over  300  volts  as  a  high  pressure, 
or  "high  potential."  As  300  volts  will  only  operate  a 
series  of  6  arc  lamps,  nearly  all  arc  lighting  circuits 
come  under  the  head  of  "high  potential."  It  is  com- 
mon practice  to  install  arc  circuits  of  50  lamps  requir- 


CENTRAL    STATIONS.  39 

ing  a  pressure  of   2,500  volts,  and  it  is  not  uncommon 
to  install  100  light  or  5,000  volt  circuits. 

Multiple  Arc  Circuits, — Suppose  now  we  attach  one 
end  of  one  wire  to  the  positive  pole  of  our  dynamo  and 
one  end  of 'another  wire  to  the  negative  pole  of  our 
dynamo,  the  other  ends  of  the  wires  being  free,  and  the 
wires  insulated  from  one  another.  As  our  circuit  is 
not  completed,  no  current  will  flow  from  one  wire  to 
the  other.  If  now  we  insert  a  lamp  between  the  two 
wires,  we  will  establish  a  circuit  from  one  pole  of  the 
dynamo  to  the  other  through  the  lamp.  A  current  will 
flow  through  one  wire  to  the  lamp,  through  the  lamp, 
and  back  along  the  other  wire  to  the  opposite  pole  of 
the  dynamo.  The  strength  of  the  current  will  be  deter- 
mined by  the  resistance  of  our  wire,  and  of  our  lamp; 
and  as  the  resistance  of  our  wire  is  in  practice  very 
small  compared  with  that  of  our  lamp,  we  may  say  that 
the  current  is  determined  by  the  pressure  of  the  dynamo 
and  the  resistance  of  the  lamp.  If  now  we  connect 
another  lamp  between  our  two  wires,  we  have  our  cir- 
cuit completed  by  two  paths,  and  the  current  will  flow 
through  each  of  them.  We  say  that  the  two  lamps  are 
connected  in  "parallel"  or  in  "multiple  arc."  We  can 
in  a  similar  manner  connect  any  number  of  lamps 
between  our  two  wires,  thus  forming  any  number  of 
return  paths.  If  each  one  of  our  lamps  has  the  same 
resistance,  the  current  will  divide  equally  between  them 
all.  It  is  customary  to  connect  up  incandescent  lamps 
in  "  multiple  arc."  The  most  common  form  of  16  c.  p. 
incandescent  lamp  requires  a  current  of  about  one-half 
an  ampere  to  operate  it  properly,  and  to  cause  this 


4O  THE    NATIONAL    ELECTRICAL    CODE. 

current  to  pass  through  the  lamp  we  require  a  pressure 
of  1 10  volts.  If  we  have  a  pressure  of  no  volts  between 
two  wires,  and  insert  such  a  lamp,  we  will  therefore  get 
a  current  through  the  dynamo,  wires  and  lamp  of  one- 
half  an  ampere.  If  we  insert  a  second  lamp,  we  will, 
if  we  still  maintain  our  pressure  at  no  volts  between 
our  wires,  also  get  a  current  of  one-half  an  ampere 
through  the  second  lamp,  so  that  our  dynamo  will  send 
out  a  current  of  one  ampere  through  the  circuit,  and 
this  current  will  be  divided  equally  between  the  two 
lamps.  In  the  same  way,  if  we  attach  any  number,  say 
100,  lamps  between  the  two  wires  in  "multiple  arc," 
we  will,  if  the  pressure  is  held  constant  at  no  volts, 
get  one-half  an  ampere  through  each  lamp,  so  that  our 
dynamo  will  be  sending  out  a  current  of  50  amperes 
through  the  circuit,  to  be  divided  equally  among  the 
100  lamps.  We  thus  see  that  the  two  connections, 
"series  "and  "multiple  arc,"  are  diametrically  oppo- 
site to  one  another.  With  one  system  (series)  our 
current  is  the  same  for  any  number  of  lamps,  but  our 
pressure  must  be  increased  as  the  number  of  lamps  is 
increased.  In  "multiple  arc"  system,  however,  the 
pressure  of  our  dynamo  remains  practically  the  same, 
no  matter  how  many  lamps  are  in  circuit,  but  each 
additional  lamp  calls  for  so  much  additional  current. 
The  system  of  lighting  with  the  lamps  in  series  is  com- 
monly called  the  "constant  current "  system,  and  the 
system  of  lighting  with  lamps  in  multiple  arc  is  called  a 
"  constant  potential  "  system.  Since  up  to  the  present 
time  the  electric  art  has  not  produced  a  satisfactory 
commercial  incandescent  lamp  that  will  stand  a  pres- 


CENTRAL    STATIONS.  41 

sure  of  over  no  to  115  volts,  current  for  incandescent 
lighting  is  usually  distributed  upon  low  potential  cir- 
cuits. Electric  motors  are  almost  universally  operated 
upon  multiple  arc  circuits,  and  at  a  pressure  of  either 
1 10,  220  or  500  volts,  220  volts  being  the  most  common 
pressure,  except  for  motors  upon  street  cars,  which  are 
almost  universally  operated  at  500  volts.  We  may 
apply  our  analogy  of  the  flow  of  water  to  illustrate  a 
series  or  multiple  arc  circuit  in  a  number  of  ways.  For 
example,  suppose  that  we  have  a  large  number  of  small 
tanks,  placed  one  directly  above  another.  If  we  have 
a  small  hole  in  the  bottom  of  each  tank,  so  that  the 
water  will  flow  from  each  tank  into  the  one  below  it,  we 
will,  upon  pumping  water  into  the  top  tank,  have  a 
current  flowing  down  through  all  the  tanlcs  in  series.  If 
we  connect  our  bottom  tank  to  a  reservoir,  and  pump 
the  water  from  the  reservoir  up  through  a  pipe  into  the 
top  tank,  we  will  have  a  fair  illustration  of  the  "  series" 
system.  Our  pump  corresponds  to  our  dynamo;  our 
pipe  to  our  wire  or  conductor,  and  our  tanks  to  our 
electric  lamps.  The  higher  we  stack  up  our  tanks,  the 
greater  must  be  the  pressure  of  our  pump  to  lift  the 
same  amount  of  water.  Our  water  pressure  corresponds 
to  our  volts,  and  the  rate  of  flow  of  water  corresponds 
to  our  amperes.  Again,  suppose  that  we  have  one  large 
tank,  with  a  great  number  of  holes  in  the  bottom;  if 
now  we  pump  water  into  this  tank  fast  enough  so  that 
we  maintain  a  constant  level  or  head  in  the  tank,  we 
shall  have  a  flow  out  of  the  tank  which  will  depend 
upon  the  number  and  size  of  the  holes.  If  our  holes 
are  all  the  same  size  and  shape,  we  will  get  the  same 


42  THE    NATIONAL    ELECTRICAL    CODE. 

flow  through  any  one  hole  as  through  each  of  the  oth- 
ers, /.  e.>  the  flow  would  be  proportionate  to  the  number 
of  holes.  If  our  tank  is  fed  by  a  pump  as  before,  the 
water  being  carried  back  into  the  tank  through  a  pipe, 
we  shall  have  a  fair  illustration  of  a  "multiple  arc" 
system.  Our  pump  (dynamo)  maintains  a  large  rate  of 
flow  (amperes)  at  a  constant  pressure  upon  bottom  of 
the  tank  of  so  many  pounds  to  the  square  inch  (volts). 
Alternating  Circuit. — Up  to  the  present  we  have 
talked  of  electricity  in  the  form  of  a  current  flowing, 
like  water  in  a  pipe,  in  one  direction.  We  have,  how- 
ever, to  consider  in  electricity  what  is  called  an  "Alter- 
nating Current,"  i.  e.,  a  current  which  flows  in  a  wire 
first  in  one  direction  and  then  in  the  other  direction. 
We  can  only  use  our  water  analogy  by  comparing  this 
kind  of  current  to  what  we  would  get  provided  we  had 
a  cylinder  containing  a  piston  and  should  connect  the 
two  ends  of  the  cylinder  to  one  another  by  a  pipe.  If 
now  the  cylinder  and  pipe  are  both  full  of  water,  we 
will  get  a  flow  in  the  pipe  with  each  movement  of  the 
piston.  If  our  piston  moves  back  and  forth,  our  cur- 
rent will  first  flow  in  one  direction,  then  cease  and  then 
flow  in  the  opposite  direction.  We  do  not,  at  this  time, 
need  to  go  further  into  a  discussion  of  the  nature  of  an 
"alternating  current"  than  to  give  this  simple  analogy. 
The  application  of  alternating  current  will  be  consid- 
ered more  fully  when  we  come  to  that  part  of  the  code 
which  considers  "alternating  systems."  For  the  pres- 
ent we  need  only  say  that  the  alternating  current  is 
used  extensively  for  incandescent  lighting,  and  to  a 
limited  extent  for  operating  arc  lamps  and  motors.  The 


CENTRAL    STATIONS.  43 

object  of  using  an  alternating  current  for  incandescent 
lamps  is  that  it  enables  us  to  operate  the  lamps  in  mul- 
tiple arc,  at  a  great  distance  from  our  dynamo,  with 
the  use  of  much  smaller  conducting  wires  than  would 
be  required  for  the  same  number  of  lamps  if  a  direct 
current  were  used.  The  higher  the  pressure  or  voltage 
at  which  we  transmit  electricity,  the  smaller  will  be  our 
wire  for  a  given  distance  of  transmission,  and  a  given 
loss  of  energy.  For  example,  suppose  we  wish  to  trans- 
mit electricity  for  1,000  sixteen-candle  electric  lamps  a 
distance  of  one  mile  with  a  loss  of  only  10  per  cent,  of 
our  power  in  overcoming  the  resistance  of  our  conduc- 
tors. If  we  undertake  to  run  our  dynamo  at  120  volts, 
and  supply  direct  current  to  our  lamps  at  a  pressure  of 
no  volts,  our  wire  will  be  of  enormous  size,  /.  <?.,  over 
two  inches  in  diameter.  If  we  could  transmit  the  same 
amount  of  electric  energy  at  a  pressure  of  1,200  volts, 
instead  of  120,  we  could,  with  the  same  loss  of  energy, 
use  a  wire  of  only  r&o  the  weight  per  foot,  or  a  wire 
having  a  diameter  of  less  than  a  quarter  of  an  inch.  As 
we  said  before,  we  cannot  secure  satisfactory  incandes- 
cent lamps  which  will  operate  at  a  pressure  of  over 
about  no  or  115  volts.  If,  however,  we  should  trans- 
mit our  electricity  at  a  high  pressure,  say  1,000  or 
2,000  volts,  and  then  transform  it  so  that  we  could  use 
it  in  our  lamps,  at  a  pressure  of  no  volts,  we  would 
save  immensely  in  the  cost  of  our  circuits.  This  we 
can  do  easily  if  we  use  an  alternating  current.  The 
alternating  current  is  therefore  used  to  enable  us  to  use 
high  pressures  on. our  outside  circuits.  As  regards  our 
Central  Station,  therefore,  the  alternating  circuit  is  a 


44  THE    NATIONAL    ELECTRICAL    CODE. 

"high  potential"  circuit.  The  code  treats  all  series 
circuits  and  all  alternating  circuits  (either  series  of  mul- 
tiple arc)  as  high  potential  circuits.  Rule  "b"  refers 
to  the  use  of  what  is  commonly  called  a  "ground 
detector."  The  most  common  form  of  this  device  con- 
sists of  two  or  more  incandescent  lamps  and  a  push 
button  for  making  a  momentary  connection  of  the  sys- 
tem to  the  earth.  If  a  system  of  conductors  is 
grounded  (/.  e.,  poorly  insulated  from  the  earth),  then 
as  soon  as  we  push  the  button  the  lamps  will  show  an 
unequal  brilliancy  which  indicates  at  once  which  pole 
of  the  circuit  is  grounded,  and  in  a  rough  way  shows 
whether  the  resistance  of  the  ground  contact  is  large  or 
small.  When  a  ground  appears  upon  a  low  potential 
system  while  the  circuits  are  in  operation,  it  can  usually 
be  measured  by  an  ordinary  portable  volt  meter.  When 
this  cannot  be  done,  the  insulation  should  be  measured 
immediately  after  shutting  down  the  station.  In  any 
event  the  ground  should  be  immediately  located  and 
promptly  removed. 

Motors. — Motors  are  subject  to  the  same  rules  con- 
cerning installation  and  maintainance  as  dynamos. 
Rule  "a  "  requires  a  double  pole  cut-out  and  a  double 
pole  switch.  This  simply  means  that  every  motor  must 
have  a  switch  by  which  an  attendant  can  disconnect  it 
completely  from  the  circuit,  and  that  it  must  be 
equipped  with  a  cut-out  or  safety  device,  which  will 
automatically  open  the  circuit  of  the  motor,  thus  cut- 
ting the  current  out  of  the  motor  if  at  any  time  the  cur- 
rent becomes  great  enough  to  over-heat  it.  It  is  one  of 
the  peculiarities  of  an  electric  motor  that  a  pressure 


CENTRAL    STATIONS.  45 

which  will  send  the  proper  amount  of  current  through 
it  when  it  is  running  at  full  speed,  will,  when  the  motor 
is  just  starting,  or  is  moving  slowly,  send  through  it  a 
current  large  enough  to  destroy  its  insulation.  This 
can  only  be  guarded  against  by  inserting  into  the  cir- 
cuit a  variable  resistance  or  ''rheostat,"  by  means  of 
which  the  current  can  be  controlled  until  the  motor  has 
gotten  its  speed.  The  resistance  box  when  used  for  this 
purpose*  is  ordinarily  called  a  "starting  rheostat,"  or 
"starting  box."  .  The  motor  should  always  be  started 
with  all  the  resistance  in  circuit,  and  the  resistance 
should  be  cut  out  gradually  as  the  speed  increases, 
until  at  full  speed  it  is  all  out.  As  the  resistance  thrown 
in  circuit  for  starting  of  motor  is  usually  made  of  wire 
of  such  a  size  that  it  will  become  very  hot  if  perma- 
nently left  in  the  circuit,  the  resistance  box  should  be 
equipped  with  a  switch  of  such  design  that  the  resist- 
ance must  always  be  all  out  of  circuit,  except  while  it  is 
being  gradually  turned  out.  The  switch  should  also' be 
so  designed  that  whenever  the  motor  circuit  is  opened, 
it  cannot  again  be  closed  except  with  the  resistance  all 
in  circuit.  Without  such  a  switch,  if  a  Central  Station 
operating  motor  should  shut  down  for  a  few  moments 
and  then  start  up  again,  there  would  be  a  liberal  dis- 
play of  fire-works  at  every  motor,  unless  there  happened 
to  be  an  attendant  on  hand  to  immediately  turn  the 
handle  of  the  rheostat.  An  attendant  is  almost  always 
on  hand  to  watch  a  dynamo  while  in  operation.  It  is 
customary,  however,  when  small  motors  are  operated, 
to  simply  have  a  man  to  inspect  them  occasionally,  per- 
haps only  a  few  times  a  day.  It  is  therefore  important 


46  THE    NATIONAL    ELECTRICAL    CODE. 

that  a  motor  should  be  installed  even  more  carefully 
than  the  dynamo,  and  should  be  protected  by  every 
available  safeguard. 


CHAPTER    V. 

CLASS    B,     HIGH    POTENTIAL     SYSTEMS.        PART    I. 

TEXT  OF  CODE  COVERED  BY  THIS  CHAPTER.  CLASS  B,  HIGH 
POTENTIAL  SYSTEMS,  OVER  300  VOLTS: — Any  circuit  attached  to  any 
machine,  or  combination  of  machines,  which  develop  over  300 
volts  difference  of  potential  between  any  two  wires,  shall  be  con- 
sidered as  a  high  potential  circuit  and  coming  under  that  class, 
unless  an  approved  transforming  device  is  used,  which  cuts  the 
difference  of  potential  down  to  less  than  300  volts. 

10.  OUTSIDE  CONDUCTORS: — All  outside,  overhead  conductors 
(including  services):  a.  Must  be  covered  with  some  approved 
insulating  material,  not  easily  abraded,  firmly  secured  to  properly 
insulated  and  substantially  built  supports,  all  tie  wires  having  an 
insulation  equal  to  that  of  the  conductors  they  confine.  (See  Defi- 
nitions.) b.  Must  be  so  placed  that  moisture  cannot  form  a  cross- 
connection  between  them,  not  less  than  a  foot  apart,  and  not  in 
contact  with  any  substance  other  than  their  insulating  supports. 
c.  Must  be  at  least  seven  feet  above  the  highest  point  of  flat 
roofs,  and  at  least  one  foot  above  the  ridge  of  pitched  roofs  over 
which  they  pass  or  to  which  they  are  attached,  d.  Must  be  pro- 
tected by  dead  insulated  guard  irons  or  zvtres  from  possibility 
of  contact  with  other  conducting  wires  or  substances  to  which 
current  may  leak.  Special  precautions  of  this  kind  must  be  taken 
where  sharp  angles  occur,  or  where  any  wires  might  possibly 
come  in  contact  with  electric  light  or  power  wires,  e.  Must  be 
provided  with  petticoat  insulators  of  glass  or  porcelain.  Porce- 
lain knobs  or  cleats  and  rubber  hooks  will  not  be  approved,  f. 
Must  be  so  spliced  or  jointed  as  to  be  both  mechanically  and  elec- 
trically secure  without  solder.  The  joints  must  then  be  soldered, 
to  insure  preservation,  and  covered  with  an  insulation  equal  to 

(47) 


48  THE    NATIONAL    ELECTRICAL    CODE. 

that  on  the  conductors.  (See  Definitions).  g-.  Telegraph,  tele- 
phone and  similar  wires  must  not  be  placed  on  the  same  cross- 
arm  with  electric  light  or  power  wires. 

11.  SERVICE  BLOCKS: — Must  be  covered  over  their  entire  sur- 
face with  at  least  two  coats  of  water  proof  paint. 

12.  INTERIOR    CONDUCTORS.       All    Interior    Conductors  : — a. 
Must  be  covered  where  they  enter  buildings  from  outside  terminal 
insulators  to  and  through  the  walls,  with  extra  waterproof  insulation, 
and  must  have  drip  loops  outside.    The  hole  through  which  the  con- 
ductor passes  must  be  bushed  with  waterproof  and  non-combustible 
insulating  tube,  slanting  upward  toward  the  inside.     The  tube  must 
be  sealed  with  tape,  thoroughly  painted,  and  securing  the  tube  to 
the  wire.     b.   Mjist  be  arranged  to  enter  and  leave  the  building 
through   a  double  contact  service  switch,  which  will  effectually 
close  the  main  circuit  and  disconnect  the  interior  wires  when  it  is 
turned  "  off.  '     The  switch  must  be  so  constructed  that  it  shall  be 
automatic  in  its  action,  not  stopping  between  points  when  started, 
and  prevent  an  arc  between  the  points  under  all  circumstances; 
it  must  indicate  on   inspection  whether  the  current  be  "on"  or 
"off,"  and  be  mounted  in  a  non-combustible  case,  and  kept  free 
from  moisture,  and  easy  of  access  to  police  or  firemen.     So  called 
"snap  switches"  shall  not  be  used  on  high  potential  circuits,     c. 
Must  be  always  in  plain  sight,  and  never  encased,  except  when 
required  by  the  inspector,     d.    Must  be  covered  in  all  cases  with 
an  approved  non-combustible   material   that  will   adhere  to  the 
wire,  not  fray  by  friction,  and  bear  a  temperature  of  150  degrees  F. 
without  softening.    (See  Definitions),    e.  Must  be  supported  on  glass 
or  porcelain  insulators,    and    kept    rigidly    at  least    eight  inches 
from    each  other,    except    within    the   structure    of  lamps  or  on 
hanger  boards,  cut-out  boxes,  or  the  like,  where  less  distance  is 
necessary,    f.    Must  be  separated  from  contact  with  walls,  floors, 
timbers  or  partitions  through  which  they  may  pass  by  non-com- 
bustible insulating  tube.     g.   Must  be  so  spliced  or  joined  as  to 
be   both  mechanically    and    electrically    secure    without    solder. 
They  must  then  be  soldered,  to  insure  preservation,  and  covered 
with  an  insulation  equal  to  that  on  the  conductors. 

DEFINITION  of  the  word  APPROVED  as  used  in  these  rules,  and 


HIGH    POTENTIAL    SYSTEMS.  49 

notice  of  the  approval  of  certain  wires  and  materials,  and  thr 
interpretation  of  certain  rules. 

RULE  10,  SECTION  a,  AND  RULE  12,  SECTION  d. — Insulation 
that  will  be  approved  for  service  wires  must  be  solid,  at  least  ^ 
of  an  inch  in  thickness,  and  covered  with  a  substantial  braid.  It 
must  not  readily  carry  fire,  must  show  an  insulating  resistance  of 
one  meghom  per  mile  after  two  weeks'  submersion  in  water  at  70 
degrees  Fahrenheit,  and  three  days'  submersion  in  lime  water, 
with  a  current  of  550  volts,  and  after  three  minutes'  electri- 
fication. 

WIRES: — The  following  list  of  wires  have  been  tested  and 
found  to  comply  with  the  requirements  for  an  approved  insulation 
under  Rule  10  a,  Rule  12  d,  and  Rule  18  a:  Acme,  Ajax,  Ameri- 
canite,  Bishop,  Canvasite,  Clark,  Columbia,  Crescent,  Crown, 
Edison  Machine,  Globe,  Grimshaw  (white  core),  Habirshaw  (red 
core),  Kerite,  National  India  Rubber  Co.  (N.  I.  R.),  Okonite, 
Paranite,  Raven  Core,  Safety  Insulated  (Requa  white  core,  Safety 
black  core),  Salamander  (rubber  covered),  Simplex  (caoutchouc), 
United  States  (General  Electric  Co.)  None  of  the  above  wires  to  be 
used  unless  protected  with  a  substantial  braided  outer  covering. 

RULE  10,  SECTION  f.  All  joints  must  be  soldered,  even  if 
made  with  the  Mclntyre  or  any  other  patent  splicing  device.  This 
ruling  applies  to  joints  and  splices  in  all  classes  of  wiring  covered 
by  these  Rules. 

As  we  have  stated,  the  high  potential  circuits  in  com- 
mon use  are,  for  the  most  part,  either  arc  circuits, 
alternating  current  incandescent  circuits,  or  electric 
railway  circuits.  Alternating  current  systems  and  street 
railway  systems  are  separately  treated  in  special  sec- 
tions of  the  code.  The  rules  laid  down  in  the  part  of 
the  code  under  consideration  apply  particularly  to  the 
installation  of  arc  light  systems. 

As  we  have  stated  in  a  previous  chapter,  arc  lights  are 
usually  operated  in  series,  and,  as  a  consequence,  an 
arc  system  is  usually  a  high  potential  system.  The 


50  THE    NATIONAL    ELECTRICAL    CODE. 

pressure  upon  arc  light  circuits  in  common  practice 
varies  from  1,000  to  5,000  volts.  From  what  we  have 
already  said  about  the  nature  of  electricity,  it  is  evi- 
dent that  the  higher  the  pressure  of  a  system  the  higher 
must  be  the  resistance  of  our  insulation  to  prevent  leak- 
age of  current.  Again,  the  higher  the  pressure,  the 
greater  the  arc  which  will  be  maintained,  in  case  the 
circuit  is  broken  or  interrupted.  The  higher  the  pres- 
sure the  greater  the  hazard  and  the  greater  must  be  the 
care  exercised  to  secure  good  insulation  and  to  prevent 
the  formation  of  an  arc  in  the  vicinity  of  combustible 
material. 

A  "service"  is  the  name  applied  to  the  wires  which 
connect  an  outside  circuit  (either  overhead  or  "under- 
ground) to  the  wires  or  conductors  within  a  building. 
According  to  section  "  a  "  of  Rule  10  and  the  definition 
applying  to  that  section,  a  high  grade  of  "moisture 
proof"  or  rubber-covered  wire  must  be  used  on  all  out- 
side high  potential  circuits.  It  is  still  the  custom,  how- 
ever, to  use  upon  pole  lines  what  is  called  "weather 
proof"  wire,  or  a  wire  covered  with  cotton  braid  satur- 
ated with  .a  water  proof  compound  or  paint.  As  long 
as  the  weather  proof  wires  stay  in  place  upon  their  insu- 
lators and  do  not  come  in  contact  with  other  wires  they 
arc  all  right,  as  both  the  surrounding  air  and  the  glass 
supports  are  the  best  of  insulators.  Nearly  all  the  arc 
circuits  about  the  country  are  of  weather-proof  wire. 
If  the  construction  is  good,  this  class  of  work  may  be 
considered  safe  and  satisfactory,  where  there  are  but 
few  wires.  In  large  cities,  however,  and  in  all  places 
where  arc  wires  cross  and  run  near  to  other  wires,  such 


HIGH    POTENTIAL    SYSTEMS.  51 

as  telephone,  telegraph  and  incandescent  wires,  the 
insulation  should  be  the  best  that  can  be  secured.  Over- 
head wires  are  fastened  to  their  supporting  insulators 
by  short  pieces  of  wire  called  tie  wires.  As  tie  wires 
are  twisted  tightly  about  the  conducting  wire,  it  is 
required  that  the  tie  wires  themselves  shall  be  of  insu- 
lated wire.  A  bare  tie  wire  easily  cuts  through  the  cov- 
ering of  our  conductor,  and  thus  destroys  our  insulation 
at  the  very  point  where  it  is  most  needed.  The  distance 
between  wires  is  determined  by  the  span  or  distance 
between  poles  and  the  space  available,  but  as  a  rule  the 
insulators  are  supported  upon  standard  cross-arms,  the 
pins  supporting  the  insulators  being  one  foot  apart. 

When  any  two  conductors  come  into  metallic  connec- 
tion with  one  another  they  are  said  to  be  "crossed" 
with  one  another,  and  the  contact  is  called  a  "cross." 
Guard  irons  or  wires  are  spoken  of  in  the  code  as  if 
there  were  two  devices  for  doing  the  same  thing.  This 
is  slightly  misleading,  as  guard  wires  are  usually 
stretched  over  live  conductors  to  prevent  other  wires 
from  falling  upon  them,  while  guard  irons  are  most 
often  used  to  prevent  conductors  from  falling  down  in 
case  they  should  become  detached  from  their  support- 
ing insulators. 

The  weak  points  in  the  insulation  of  wires  on  a  pole 
line  are  where  the  wires  are  tied  to  the  insulators ;  and 
as  the  best  of  insulation  deteriorates  with  age  and  is 
liable  to  mechanical  injury,  we  must  depend  for  our 
insulation  chiefly  upon  our  insulators. 

The  ordinary  green  glass  insulator  which  we  see 
screwed  upon  a  pin  driven  into  a  cross  arm  is  a  "pet- 


52  THE    NATIONAL    ELECTRICAL    CODE. 

ticoat "  insulator.  These  insulators  extend  down  below 
the  point  where  the  pin  screws  in,  forming  an  umbrella 
or  "petticoat,"  thus  keeping  the  top  of  the  pin  and  the 
bottom  of  the  insulator  dry  even  when  it  rains  or  snows. 
When  freshly  made,  a  good  "twist"  or  "Western 
Union  "  joint,  made  by  twisting  the  wires  tightly  to- 
gether, forms  a  perfectly  good  connection  both  elec- 
trically and  mechanically,  if  carefully  made  ;  but  such 
a  joint  will  work  loose  from  swinging  or  from  expansion, 
the  surface  of  the  wire  will  corrode  and  the  joint  will 
offer  a  high  resistance  to  the  passage  of  the  current. 
Solder  should  therefore  be  used  on  all  joints;  for  where- 
ever  there  is  resistance,  energy  is  lost  and  heat  is  gen- 
erated. The  Mclntyre  connector  referred  to  in  the 
definition  explanatory  of  section  "  f  "  is  a  patent  device 
for  joining  wires  and  making  a  tight  joint  quickly;  but 
with  a  joint  thus  made,  as  with  any  other  joint,  the 
contact  depends  upon  the  skill  and  care  of  the  man 
making  the  joint  and  solder  is  the  best  thing  to  secure 
a  sure  and  permanent  joint 

Interior  Conductors, — At  all  points  where  wires  enter 
buildings,  special  pains  must  be  taken  to  secure  good 
insulation,  as  the  wire  at  these  points  is  liable  to  have 
its  insulation  mechanically  injured  unless  it  is  firmly 
secured  in  place;  and  again,  where  a  wire  goes  through 
a  wall  it  is  pretty  sure  to  come  in  contact  with  moisture 
unless  it  is  specially  protected.  Where  the  wires  go 
through  a  wooden  wall,  it  is  of  course  impossible  to 
keep  them  far  away  from  the  wood,  and  unless  they  are 
surrounded  by  a  non-inflammable  insulation,  there  is 
always  a  hazard.  Tubes  for  surrounding  high  potential 


HIGH    POTENTIAL    SYSTEMS.  53 

wires  should  be  of  glass,  porcelain  or  vitrified  earthen 
ware. 

A  "drip  loop,"  as  its  name  indicates,  is  a  downward 
bend  in  the  wire  just  outside  the  building.  By  allowing 
our  insulating  tube  to  project  through  the  wall  and  to 
slant  upward  toward  the  inside,  and  by  giving  the  water 
a  chance  to  drip  off  a  sharp  bend  in  the  wire  outside 
the  building,  we  can  effectually  prevent  any  water  from 
following  the  wire  into  the  building.  As  we  have  said, 
nearly  all  the  high  pressure  wires  which  enter  buildings 
are  arc  wires. 

Section  "b  "  describes  an  arc  light  switch.  As  arc 
lights  are  usually  operated  in  series,  if  we  cut  out  a 
light  or  a  number  of  lights  with  a  switch  we  will  open 
our  circuit  and  thus  put  out  all  the  lights  upon  the  cir- 
cuit, unless,  at  the  same  time,  we  close  the  circuit 
through  some  other  path.  An  arc  light  switch  is, 
therefore,  so  designed  that  it  provides  a  new  path  for 
the  current  before  it  opens  the  circuit  to  the  lamps 
which  it  controls.  A  "snap"  switch  is  the  name 
applied  to  the  small  round  switch  such  as  is  commonly 
used  for  controlling  small  groups  of  incandescent  lamps. 
These  switches  are  not  so  constructed  as  to  break  a 
high  potential  current  without  arcing.  As  they  are 
generally  made,  an  arc  of  this  kind  would  destroy  the 
switch  and  endanger  any  adjacent  wood  work.  A  switch 
is  rendered  "  automatic  "  in  its  action  by  so  designing 
it  that,  when  its  handle  is  moved,  a  spring  throws  the 
switch  so  as  to  either  close  or  to  completely  open  the 
circuit.  Section  "  d  "  requires  that  high  pressure  wires 
must  be  run  in  sight,  i.  <?.,  what  is  known  as  "open 


54  THE    NATIONAL    ELECTRICAL    CODE. 

wiring  "  must  be  used.  It  is  a  general  rule  that  open 
wiring  is  always  safer  than  concealed  wiring,  except 
where  it  is  necessary  to  cover  the  wires  to  secure 
mechanical  protection.  For  interior  conductors  noth- 
ing except  moisture  proof  wire  should  ever  be  used.  A 
"  megohm  "  (referred  to  in  the  definition  of  Rule  10, 
section  "a"),  is  equal  to  1,000,000  ohms. 

The  insulation  resistance  of  a  wire  is  usually  tested 
by  immersing  the  wire  in  a  tank  of  water  and  measur- 
ing the  resistance  between  the  water  and  the  ends  of 
the  wire,  which  are  kept  dry  and  well  out  of  the  water. 
The  greater  the  length  of  a  wire  the  greater  will  be  the 
leakage,  or  what  amounts  to  the  same  thing,  the  less 
will  be  the  insulation  resistance;  so  that  the  code  prop- 
erly requires  a  certain  insulation  resistance  per  mile. 
Not  only  should  none  but  approved  wires  be  used,  but 
we  should  bear  in  mind  that  all  of  the  wires  "ap- 
proved "  are  not  of  the  same  grade.  In  fact,  the  list 
in  the  code  includes,  in  some  cases,  more  than  one 
grade  of  wire  made  by  the  same  manufacturer.  Section 
"e"is  important;  but  while  it  is  important  that  the 
wires  shall  be  separated  a  proper  distance,  it  is  still 
more  important  that  the  wires  shall  be  so  supported 
that  they  will  always  be  held  rigidly  apart.  Section 
"f  "  (which  applies  also  to  wires  of  low  potential),  is  a 
very  important  requirement.  If  sections  "e-"  and  "f" 
are  strictly  observed,  there  will  be  no  danger  of  heat 
being  conveyed  to  wood  work,  even  though  the  wires 
become  excessively  hot,  unless  the  insulation  of  the 
wire  itself  takes  fire.  The  first  requirement  of  section 
"g"  is  for  protection  against  poor  workmanship.  The 


HIGH    POTENTIAL    SYSTEMS.  55 

clause  concerning  insulation  of  joints  has  already  been 
discussed.  Although  it  calls  for  what  is  practically  an 
impossibility,  still  this  section  is  an  important  one,  as 
it  directs  our  attention  to  the  fact  that  #// joints  should 
be  avoided  as  far  as  is  possible  (except  when  they  come 
in  the  air  between  insulators),  and  when  they  cannot  be 
avoided,  they  should  be  just  as  good  as  material  and 
skill  can  make  them. 


CHAPTER   VI. 

HIGH    FOTENTTA7,    SYSTEMS.       PART    II. 

TEXT  OF  CODE  COVERED  BY  THIS  CHAPTER.  LAMPS  AND 
OTHER  DEVICES.  13.  ARC  LAMPS— In  every  case: — a.  Must  be 
carefully  insulated  from  inflammable  material,  b.  Must  be  pro- 
vided at  all  times  with  a  glass  globe  surrounding  the  arc,  securely 
fastened  upon  a  closed  base.  No  broken  or  cracked  globes  to  be 
used.  c.  Must  be  provided  with  an  approved  hand  switch,  also 
an  automatic  switch,  that  will  shunt  the  current  around  the  car- 
bons should  they  fail  to  feed  properly,  d.  Must  be  provided  with 
reliable  stops  to  prevent  carbons  from  falling  out  in  case  the 
clamps  become  loose.  (See  Definitions.)  e.  Must  be  carefully 
insulated  from  the  circuit  in  all  their  exposed  parts,  f.  Must  be 
provided  with  a  wire  netting  around  the  globe,  and  an  approved 
spark  arrester  above  to  prevent  escape  of  sparks,  melted  copper 
or  carbon,  where  readily  inflammable  material  is  in  the  vicinit) 
of  the  lamps.  It  is  recommended  that  plain  carbons,  not  copper- 
plated,  be  used  for  lamps  in  such  places.  (See  Definitions.) 
g.  Hanger-boards  must  be  so  constructed  that  all  wires  and 
current-carrying  devices  thereon  shall  be  exposed  to  view  and 
thoroughly  insulated  by  being  mounted  on  a  waterproof,  non- 
combustible  substance.  All  switches  attached  to  the  same  must 
be  so  constructed  that  they  shall  be  automatic  in  their  action,  not 
stopping  between  points  when  started,  and  preventing  an  arc 
between  points  under  all  circumstances,  h.  Where  hanger  boards 
are  not  used,  lamps  to  be  hung  from  insulated  supports  other  than 
th«ir  conductors. 

14.  INCANDESCENT  LAMPS  IN  SERIES  CIRCUITS  HAVING  A  MAX- 
IMUM POTENTIAL  OF  300  VOLTS  OR  OVER: — a.  Must  be  governed 
by  the  same  rules  as  for  arc  lights,  and  each  series  lamp  provided 

(56) 


HIGH    POTENTIAL    SYSTEMS.  57 

with  an  approved  hand  spring  switch  and  automatic  cut-out. 
b.  Must  have  each  lamp  suspended  from  a  hanger  board  by  means 
of  a  rigid  tube.  c.  No  electro  magnetic  device  for  switches  and 
no  system  of  multiple  series  or  series  multiple  lighting  will  be 
approved.  d.  Under  no  circumstances  can  series  lamps  be 
attached  to  gas  fixtures. 

DEFINITIONS.— RULE  13.  ARC  LAMPS:  — Section  c.  The  hand 
switch  to  be  approved,  if  placed  anywhere  except  on  the  lamp 
itself,  must  comply  with  requirements  for  switches  on  hanger 
boards  as  laid  down  in  Section  "  g  "  of  Rule  13.  Section  f.  An 
approved  spark  arrester  is  one  which  will  so  close  the  upper 
orifice  of  the  globe  that  it  will  be  impossible  for  any  sparks  thrown 
off  by  the  carbon  to  escape. 

LAMPS    AND    OTHER    DEVICES. 

Arc  Lamps. — The  arc  of  an  arc  lamp,  like  any  elec- 
tric arc,  consists  of  a  flame  which  gives  a  most  intense 
heat.  The  arc  is  maintained  between  the  ends  of  two 
rods  or  pencils  of  carbon,  commonly  called  "carbons." 
The  arc  gradually  burns  away  the  carbons,  so  that  there 
is  a  constant  combustion  going  on  all  the  time  that  the 
lamp  is  burning.  As  the  arc  is  a  source  of  heat,  it  is 
evident  that  the  lamp  must  be  so  protected  that  no 
inflammable  substance  can  ever  come  in  contact  with 
the  arc.  If  the  arc  is  not  protected  from  a  draught,  or 
if  the  carbons  are  not  perfectly  uniform  in  composi- 
tion, sparks  will  be  given  off  from  the  burning  carbon. 
Again,  the  carbons  become  white  hot  on  the  ends  for 
some  distance  from  the  arc;  so  that  if  a  carbon  should 
break  or  get  loose  and  fall  from  its  holder,  it  would 
readily  ignite  any  inflammable  substance  that  might  be 
below  the  lamp.  The  use  of  a  glass  globe  surrounding 
the  arc  is  therefore  absolutely  essential,  to  prevent  the 


58  THE    NATIONAL    ELECTRICAL    CODE. 

possibility  of  fire  from  sparks  or  falling  carbons,  when- 
ever a  lamp  is  burned  anywhere  near  combustible  mate- 
rial. Since  a  globe  is  necessary,  it  is  evident  that  it  is 
necessary  that  the  globe  shall  not  be  broken,  and  that 
a  globe  should  be  discarded  as  soon  as  it  becomes 
cracked.  A  white  or  "  opal  "globe  is  useful  for  toning 
down  and  diffusing  the  light  of  an  arc  lamp,  and  any 
globe  serves  to  protect  the  arc  from  wind  or  draughts 
which  would  interfere  with  the  steadiness  of  the  light; 
and  very  often  people  overlook  the  fact  that  the  globe 
is  still  more  useful  in  securing  safety.  We  have  seen 
that  in  arc  lighting  the  lamps  are  usually  connected 
"in  series/'  and  that  the  dynamo  maintains  a  constant 
current  in  the  circuit.  A  circuit  of  2,000  candle  power 
lamps,  for  example,  will  always  carry  a  current  of  about 
10  amperes.  If  now,  while  the  current  is  kept  constant, 
we  join  any  two  points  of  the  circuit  by  a  wire  or 
conductor,  we  shall  form  a  second  path  for  the  cur- 
rent between  these  points.  The  current  will  divide 
between  the  two  paths.  We  say  that  the  current  has 
been  "shunted  "  out  of  the  first  path  or  conductor,  and 
we  call  the  second  conducting  path  a  "shunt."  When 
a  shunt  is  placed  upon  a  portion  of  a  circuit,  the  cur- 
rent will  divide  between  the  circuit  and  the  shunt,' 
according  to  their  relative  resistances.  Whichever 
path  has  the  higher  resistance,  will  have  the  smaller 
current.  If  the  resistance  of  the  shunt  is  only  a  small 
fraction  of  the  resistance  of  the  original  path,  the  cur- 
rent will  practically  all  flow  through  the  shunt.  If, 
therefore,  we  wish  to  cut  the  current  out  of  an  arc  light 
(in  a  series  circuit),  we  have  only  to  connect  the  two 


HIGH    POTENTIAL    SYSTEMS.  59 

points  where  the  current  enters  and  where  it  leaves  the 
lamp  by  a  low  resistance  shunt.  This  is  done  in  prac- 
tice by  connecting  the  ends  of  the  wires  leading  to  and 
from  the  lamp  to  the  two  sides  of  a  switch,  so  that, 
upon  closing  the  switch,  the  current  will  flow  through 
the  low  resistance  path  presented  by  the  switch,  instead 
of  through  the  lamp,  which  has  a  comparatively  enor- 
mous resistance.  An  arc  lamp  is  quite  a  complicated 
piece  of  mechanism.  As  the  carbons  are  actually 
burned  away,  the  arc  in  a  lamp  would  gradually  grow 
longer,  until  it  got  so  long  that  it  would  break,  if  the 
carbons  were  rigidly  fixed  in  position.  An  arc  lamp  is 
therefore  provided  with  a  feeding  device.  By  means  of 
this  device,  as  fast  as  the  carbons  are  burned  away, 
they  are  automatically  fed  toward  one  another,  so  thai 
they  are  always  separated  by  about  the  same  distance. 
If  the  feeding  device  should  fail  to  work  properly,  the 
arc  would  grow  longer  and  longer,  until  at  last  it  would 
break  and  the  current  would  go  through  the  fine  wires 
in  the  lamp,  burning  off  its  insulation  and  maintaining 
a  fire  until  it  had  opened  the  circuit. 

To  prevent  such  an  occurrence,  the  code  requires  in 
Rule  "  c  "  that  the  lamp  shall  be  provided  with  an  auto- 
matic switch  in  addition  to  the 'hand  switch.  The  hand 
switch  is  used  to  shunt  the  current  around  the  two  ter- 
minals where 'the  wires  are  joined  to  the  lamp,  thus 
cutting  the  current  out  of  the  lamp  altogether.  The 
automatic  switch  (which  is  a  part  of  the  lamp  mechan- 
ism) is  used  to  shunt  the  current  around  the  gap  formed 
between  the  carbons  whenever  the  a^c  is  broken  and 
not  immediately  re-established.  The  automatic  switch 


60  THE    NATIONAL    ELECTRICAL    CODE. 

is  essentially  a  safety  device.  Rule  "  d  "  refers  to  the 
proper  design  of  the  lamp  itself.  Some  old  style  lamps 
were  so  constructed  that  if  a  lower  carbon  became 
loose,  it  could  fall  out  of  the  lamp.  The  danger  due 
to  such  construction  is  evident.  Rule  £<e"  should  be 
observed  for  protection  against  fire,  and  also  to  prevent 
a  hazard  to  life.  Indirectly  a  hazard  to  life  is  a  hazard 
to  property;  for  if  there  is  danger  to  life  in  handling 
an  electric  device  or  machine,  the  probability  is  that 
the  machine  or  device  will  not  receive  proper  care  and 
attention,  and  almost  any  electrical  apparatus  which  is 
not  kept  clean  and  in  good  working  order  is  liable  to 
become  a  source  of  danger.  Rule  «f "  is  one  that 
should  be  rigidly  enforced.  An  arc  lamp  should  always 
be  completely  enclosed,  when  anywhere  near  combusti- 
ble material.  The  object  of  a  wire  netting  about  a 
globe  is  to  prevent  a  globe  from  falling  to  pieces  in  the 
event  of  its  becoming  cracked.  Experience  has  often 
demonstrated  the  fact  that  a  globe  open  at  the  top  is 
not  sufficient  protection  against  the  escape  of  sparks. 
Arc  light  carbons  are  often  covered  (by  plating)  with  a 
thin  coating  of  copper.  Under  certain  conditions, 
coated  carbons  give  better  results;  but  the  coating  may 
increase  the  breakage  of  globes;  especially  if  the  coat- 
ing is  unnecessarily  thick,  as  is  sometimes  the  case.  If 
a  lamp  is  not  properly  "  trimmed,"  that  is  to  say,  if  the 
carbons  are  not  of  the  right  length  or  are  not  properly 
adjusted,  the  arc  will  sometimes  consume  the  entire 
lower  carbon  and  a  part  of  the  lower  clamp  or  carbon 
holder,  before  it  is  automatically  interrupted.  This 
sort  of  an  accident  is  liable  to  break  the  globe.  Natu- 


HIGH    POTENTIAL    SYSTEMS.  6l 

rally,  any  hot  carbon  or  molten  metal  that  can 
break  a  globe  may  cause  combustion  after  a  globe  is 
broken. 

A  "  hanger  board,"  like  a  "switch  board,"  was  orig- 
inally a  veritable  board.  The  ordinary  form  of  hanger 
board  consisted  of  a  small  board  from  which  the  lamp 
was  suspended  when  used  for  inside  lighting.  The 
board  carried  a  switch  and  metal  connectors  or  "  bind- 
ing posts,"  to  which  the  wires  of  the  circuit  and  the 
wires  of  the  lamp  were  connected.  The  hanger  board 
was  generally  screwed  or  nailed  directly  to  the  ceiling. 
These  hanger  boards  proved  to  be  a  danger  point,  and 
many  a  fire  was  caused  in  them  by  poor  contacts  and 
moisture.  In  selling  a  plant,  the  hanger  boards  were 
generally  included  in  the  price  of  the  lamps  and 
dynamo,  so  that  the  manufacturers  vied  with  one 
another  in  trying  to  see  who  could  produce  the  cheap- 
est; board.  It  is  surprising  to  see  how  well  they  suc- 
ceeded. A  ceiling  is  a  bad  place  for  any  electrical 
device,  and  it  has  at  last  become  apparent  that  hanger 
boards  must  be  fireproof  \.\\e  same  as  other  switch  boards 
and  switches.  The  only  suitable  materials  at  present 
applied  to  their  construction  are  marble,  slate  and  por- 
celain. It  has  in  the  past  been  common  practice  to 
support  lamps  by  hanging  them  from  the  two  conduct- 
ing wires.  These  wires  are  always  more  than  strong 
enough  to  support  the  weight  of  a  lamp;  and  at  first 
thought  it  seems  as  if  the  use  of  another  suspending 
wire  detracted  from  the  appearance  of  the  installation 
and  was  a  waste  of  labor  and  material. 

This  kind  of  construction,  although  neat  in  appear- 


62  THE    NATIONAL    ELECTRICAL    CODE. 

ance,  is  not  the  safest.  If  a  supporting  conducting 
wire  becomes  loosened  from  its  connection  to  the  lamp 
so  that  the  weight  of  the  lamp  pulls  it  away  from  the 
wire,  an  arc  will  be  formed  between  the  wire  and  the 
connector  on  the  lamp,  and  this  arc  may  be  long  and 
destructive.  Such  an  arc  will  throw  off  melted  copper 
and  create  the  worst  kind  of  a  hazard. 

Incandescent  Lamps  on  Series,  High  Potential,  Cir- 
cuits.— Our  readers  are  doubtless  all  familiar  with  the 
incandescent  lamp;  but  it  may  not  be  out  of  place  to 
call  attention  to  the  distinction  between  an  arc  and  an 
incandescent  lamp.  While  the  ends  of  the  carbons  in 
an  arc  lamp  become  incandescent  or  white-hot,  this 
incandescence  is  not  the  principal  source  of  its  light. 
Nearly  all  the  light  is  given  off  by  the  arc  or  flame. 
The  arc  is  accompanied  by  combustion,  the  carbons 
being  burned  up  as  effectually  as  coal  in  a  stove,  and 
so  rapidly  that  they  last  but  a  few  hours.  In  an  incan- 
descent lamp,  on  the  other  hand,  there  is  no  combus- 
tion. We  have  found  that  in  any  conductor  carrying 
current,  energy  is  absorbed  by  something  analogous  to 
friction.  This  energy  is  transformed  into  heat  which 
raises  the  temperature  of  the  conductor.  The  greater 
the  resistance  of  the  conductor  and  the  greater  the  cur- 
rent, the  greater  will  be  the  heat  generated  in  the  con- 
ductor. If  we  take  a  thin  copper  wire  we  can  readily 
heat  it  red  hot  with  a  few  amperes.  With  a  little  more 
current  it  is  heated  white  hot  or  incandescent.  It  now 
becomes  a  source  of  light.  If  we  make  our  conductor 
of  some  material  which  (unlike  copper)  is  a  poor  con- 
ductor, a  very  small  current  will  suffice  to  heat  it  up  to 


HIGH    POTENTIAL    SYSTEMS.  63 

incandescence.  The  loop  or  "  filament "  in  an  incan- 
descent lamp,  is  such  a  thin  high  resistance  conductor. 
The  filament  is  made  of  carbon,  a  material  which  has  a 
high  resistance  and  which  becomes  white  hot  at  com- 
paratively low  temperature.  The  light  is  given  off 
wholly  by  the  incandescence  of  the  filament.  There  is 
no  combustion,  for  combustion  would  destroy  the  fila- 
ment. Combustion  is  prevented  by  placing  the  fila- 
ment in  a  hermetically  sealed  glass  chamber  from  which 
the  air  has  been  exhausted  so  as  to  leave  an  almost  per- 
fect vacuum.  Incandescent  lamps  are,  as  we  have 
already  said,  usually  operated  "in  multiple"  and  upon 
low  potential  circuits.  There  are  many  reasons  for  this. 
The  operating  of  incandescent  lamps  in  series,  upon  a 
large  scale  presents  many  engineering  difficulties. 
While  arc  lamps  are  handled  almost  exclusively  by  men 
employed  in  lighting  stations  or  plants,  incandescent 
lamps  are  handled  by  people  who  could  not  with  safety 
to  themselves  handle  any  device  using  a  high  potential 
current.  Again  incandescent  lamps  are  used  in  many 
places  where  it  would  be  practically  impossible  to  pre- 
vent their  causing  a  great  hazard,  if  operated  upon  a 
high  potential  circuit.  There  are,  however,  a  few  spe- 
cial cases  where  it  is  desirable  to  operate  incandescent 
lamps  in  this  manner;  as,  for  example,  in  street  lighting 
and  where  the  operating  of  a  few  incandescent  lamps 
on  an  arc  circuit  will  save  the  installation  of  expensive 
circuits  or  an  extra  dynamo.  In  such  cases  we  can 
secure  safety  by  following  as  closely  as  possible  the 
rules  governing  the  installation  of  arc  light  circuits. 
Multiple  Series, — Series  Multiple. These  terms  will 


64  THE    NATIONAL    ELECTRICAL    CODE. 

be  most  easily  understood  from  examples  of  their  appli- 
cation in  practice. 

The  most  common  form  of  i6-candle  power  incandes- 
cent lamp  requires  a  current  of  about  y%  an  ampere. 
If  we  connect  20  of  such  lamps  in  parallel  or  multiple 
with  one  another  the  group  will  of  course  take  a  cur- 
rent of  about  10  amperes.  We  can  if  we  wish  supply 
these  lamps  with  their  proper  current  by  inserting  the 
group  into  an  arc  light  circuit  which  is  carrying  10 
amperes.  If  we  connect  up  a  number  of  groups  in  this 
manner,  the  lamps  in  one  group  being  in  multiple  with 
one  another,  and  the  groups  being  in  series  with  one 
another,  we  say  that  the  lamps  are  connected  in  multi- 
ple series. 

Again  the  ordinary  incandescent  lamp  is  operated  at 
a  pressure  of  about  no  volts.  If  we  connect  five  of 
such  lamps  in  series  we  must  have  a  pressure  of  550 
volts  to  have  them  burn  properly.  We  can  burn  the 
lamps  by  connecting  the  series  between  the  two  wires 
of  a  550  volt  multiple  arc  system,  such  as  is  used  for 
operating  street  railway  motors.  We  can- thus  connect 
up  any  number  of  series  in  multiple  with  one  another 
and  we  describe  the  arrangement  by  saying  that  the 
lamps  are  connected  in.  series  multiple.  The  meaning 
of  these  terms  may  be  easily  remembered  by  noting 
that  multiple  series  means  multiples  in  series,  and  series 
multiple  series  in  multiple.  The  first  word  applies  to 
the  connection  of  the  individuals  and  the  second  to  the 
arrangement  of  the  groups.  The  method  and  devices 
used  for  controlling  and  protecting  lamps  connected  in 
series  or  in  multiple,  or  for  preventing  their  creating  a 


HIGH    POTENTIAL    SYSTEMS.  65 

hazard,  do  not  apply  to  their  use  in  multiple  series  or 
series  multiple.  The  complicated  devices  which  have 
in  the  past  been  applied  to  such  systems,  for  the  pur- 
pose of  securing  good  service  and  safety,  have  them- 
selves been  sources  of  annoyance  and  danger.  The  use 
of  these  systems  is  therefore  forbidden.  This  prohibi- 
tion however  does  not  cause  any  hardship,  as  there  are 
now  many  better  and  more  simple  ways  of  securing  all 
the  advantages  that  were  sought  by  their  use.  The  first 
clause  of  section  "  c  "  is  undoubtedly  aimed  at  the  use 
of  any  ''ingenious  "  and  complicated  device  introduced 
to  do  something  that  can  be  done  more  simply  and 
safely  by  hand.  The  form  of  incandescent  lamp 
adapted  to  series  lighting  requires  a  low  voltage,  but 
takes  a  current  of  several  amperes.  It  is  not  possible 
to  protect  lamps  in  series  by  the  simple  safety  devices, 
s-ich  as  are  used  on  lamps  when  connected  in  multiple; 
and  on  a  series  system,  an  arc  which  might  be  set  up 
by  defective  insulation  in  the  fixture,  would  probably 
not  be  extinguished  until  it  had  burned  itself  out.  In  so 
doing,  it  might  at  the  same  time  easily  burn  a  hole  or 
two  in  the  gas  "pipe.  A  study  of  the  devices  used 
in  ordinary  incandescent  light  construction  will  show 
how  necessary  are  sections  "c"  and  "d"  of  Rule  14. 


CHAPTER   VII. 

CLASS    C,    LOW    POTENTIAL    SYSTEMS.       PART    I. 

TEXT  OF  CODE  COVERED  BY  THIS  CHAPTER.  CLASS  C,  Low 
POTENTIAL  SYSTEMS,  300  VOLTS  OR  LESS.  OUTSIDE  CONDUCT- 
ORS. 15.  OUTSIDE  OVERHEAD  CONDUCTORS: — a.  Must  be  erected 
in  accordance  with  the  rules  for  high  potential  conductors,  b. 
Must  be  separated  not  less  than  12  inches,  and  be  provided  with 
an  approved  fusible  cut-out,  that  will  cut  off  the  entire  current  as 
near  as  possible  to  the  entrance  to  the  building  and  inside  the 
walls. 

RULE  15.  OUTSIDE  OVERHEAD  CONDUCTORS: — Section  b.  An 
approved  fusible  cut-out  must  comply  with  the  sections  of  Rules 
23  and  24,  describing  fuses  and  cut-outs.  The  cut-out  required 
by  this  section  must  be  placed  so  as  to  protect  the  switch  required 
by  Rule  17. 

Outside  Conductors. — Low  potential  systems  include 
circuits  for  supplying  incandescent  lamps  and  power  at 
short  distances.  Incandescent  lamps  on  direct  current 
systems  are  usually  operated  at  no  volts.  On  alternat- 
ing current  systems  they  are  operated  at  either  about 
50  or  about  100  volts.  It  is  becoming  common  prac- 
tice to  operate  arc  lamps,  two  in  series,  upon  the  same 
system  of  conductors  as  no  volt  incandescent  lamps. 
The  highest  pressure  in  common  use  in  plants  that 
come  under  the  head  of  low  potential  systems  is  about 
220  volts.  Many  central  stations  operate  no  volt 
lamps  upon  what  is  called  a  "three-wire  system,"  to 

(66) 


LOW    POTENTIAL    SYSTEMS.  67 

distinguish  it  from  an  ordinary  multiple  arc  or  "two- 
wire  system  "and  from  "multiple  series  "  or  "series 
multiple  "  systems. 

The  three-wire  system  is  rather  difficult  to  understand 
from  a  brief  description  unaccompanied  by  a  diagram. 
The  object  of  using  a  three-wire  system  is  to  save  cop- 
per. By  its  use  we  can  operate  the  same  number  of 
lamps,  without  greater  loss  of  energy,  upon  a  much 
smaller  wire  than  would  be  required  for  a  two-wire  sys- 
tem. Suppose  that  we  connect  the  lamps  of  a  plant  in 
two  equal  groups,  each  group  having  its  lamps  con- 
nected in  multiple  arc  and  each  group  having  its  own 
dynamo.  If,  now,  we  connect  the  two  groups  in  series 
with  one  another  throughout,  or,  what  is  the  same 
thing,  use  a  common  wire  for  the  positive  of  one  group 
and  the  negative  of  the  other  group,  we  shall  have  a 
three-wire  system.  The  Wire  common  to  both  groups 
we  call  the  neutral  wire.  The  other  two  wires  are 
called  the  positive  and  negative  wires,  respectively,  or, 
when  spoken  of  together,  they  are  called  simply  the 
outside  wires.  By  making  a.  diagram  of  the  above 
arrangement,  the  reader  will  see  that  we  have  a  voltage 
of  220  volts  between  the  two  outside  wires  of  a  three- 
wire  system  using  no  volt  lamps.  This  system  is  used 
in  most  of  the  direct  current  central  stations  in  this 
country.  In  operating  motors  from  a  three-wire  sta- 
tion, they  are  usually  designed  to  operate  at  220  volts, 
and  are  connected  in  between  the  two  outside  wires. 
This  practice  has  led  to  the  common  use  of  220  volt 
motors,  so  that  this  voltage  is  quite  generally  used  for 
operating  stationary  motors,  where  they  are  not  too  far 


68  THE    NATIONAL    ELECTRICAL   CODE. 

from  the  generators.  By  far  the  greater  proportion  of 
all  low  potential  circuits  are  incandescent  lighting  cir- 
cuits. Arc  lamps  and  motors,  where  used  on  low 
voltages,  are  usually  connected  to  incandescent  light- 
ing systems. 

One  would  naturally  expect,  from  what  we  have  said 
about  the  importance  of  high  insulation  and  the  dif- 
ficulty of  securing  it  on  high  pressure  systems,  that  it 
would  be  a  comparatively  simple  thing  to  secure  safety 
on  a  low  potential  system,  and  that  the  rules  concern- 
ing the  installation  of  low  potential  circuits  would  be 
few  and  brief.  On  the  contrary,  we  find  the  greater 
portion  of  the  code  devoted  to  this  class  of  work.  The 
reason  for  this  is,  that  high  pressure  arc  circuits  are 
generally  located  out  in  the  street;  or,  if  the  lamps  are 
inside,  the  wires  are  run  exposed  upon  glass  or  porce- 
lain knobs,  where  they  can  be  readily  inspected.  In 
incandescent  lighting,  on  the  other  hand,  the  lamps  are 
used  mostly  for  inside  lighting,  and  they  are  placed  in 
every  conceivable  kind  of  place  and  position.  Again, 
the  incandescent  lamps  call  for  a  multiplicity  of  wires, 
and  these  wires  must  usually  be  concealed  in  some 
manner  to  prevent  their  marring  the  appearance  of 
interiors.  Safety,  under  these  trying  conditions,  requires 
the  use  of  a  high  grade  of  insulation  upon  our  wires, 
careful  and  intelligent  workmanship,  and  well  designed 
appliances  in  the  line  of  fixtures,  switches,  cut-outs, 
etc.  While  high  voltage  places  a  great  strain  upon 
insulation,  powerful  currents,  such  as  we  have  upon 
circuits  carrying  many  incandescent  lights,  represent  an 
immense  amount  of  energy;  and  the  fire  hazard  of  elec- 


LOW    POTENTIAL    SYSTEMS.  69 

tricity  is  simply  the  danger  of  transforming  the  energy 
of  an  electric  current  into  heat  in  the  wrong  place.  The 
code  applies  the  same  rules  to  outside  conductors  of 
low  as  of  high  potential  systems.  It  is  related  that  the 
laws  of  Draco  imposed  the  same  penalty  for  the  pun- 
ishment of  all  crimes,  /.  e.,  death.  This  severity  was 
justified  by  the  argument  that  the  least  of  crimes 
deserved  death,  and  that  there  was  no  more  severe 
penalty  which  could  be  applied  to  the  punishment  of 
the  greater  crimes.  Some  such  logic  as  this  was  doubt- 
less used  by  those  who  framed  the  rules  concerning 
outside  overhead  conductors.  From  an  insurance 
man's  standpoint,  about  all  that  can  be  said  concerning 
the  insulation  of  outside  conductors,  either  overhead  or 
underground,  is  that  the  better  the  insulation  outside, 
the  less  will  be  the  danger  of  fire  from  any  accident  or 
defect  on  inside  circuits  (excepting,  perhaps,  danger 
from  lightning).  If  we  so  protect  our  circuits  that  no 
trouble  on  the  outside  can  cause  a  hazard  inside  a 
building,  and  then  require  as  good  insulation  on  out- 
side conductors  as  can  be  secured  without  an  expense 
that  would  impose  an  unreasonable  hardship  upon  the 
central  station  company,  we  shall  be  following  what  is 
at  present  the  best  practice.  The  one  thing  most 
important  to  observe  is  that  low  potential  wires  which 
enter  a  building  must  be  protected  from  any  possible 
contact  with  any  high  potential  wires  outside  the  build- 
ing, as  any  such  contact  creates  a  fire  hazard  and  is  a 
menace  to  human  life.  Rule  15  brings  up  for  the  first 
time  the  " fusible  cut-out."  As  in  series  arc  work  we 
protect  our  lamp  by  two  devices — first,  a  switch  by 


70  THE    NATIONAL    ELECTRICAL    CODE. 

which  the  current  is  cut  out  of  the  lamp  by  hand,  and, 
second,  an  automatic  device  to  automatically  cut  the 
current  out  of  the  lamp  in  case  of  trouble ;  so,  in 
incandescent  lighting,  we  must  protect  our  circuits, 
first,  by  hand  switches,  and,  second,  by  automatic  cut- 
outs which  interrupt,  and  thus  cut  the  current  out  of, 
the  circuits  to  be  protected. 

We  must  always  aim  to  keep  clear  in  our  minds  the 
difference  between  arc  and  incandescent  work.  While 
both  systems  require  good  insulation  and  hand  and 
automatic  control,  we  find,  at  every  turn,  that  their 
conditions  and  requirements  are  diametrically  opposite 
in  many  respects.  In  arc  work  we  have  series  connec- 
tions; in  incandescent  work  we  have  multiple  connec- 
tions. In  arc  work  we  have  a  constant  current  and  a" 
pressure  varying  with  the  number  of  lamps.  In  incan- 
descent work  we  have  a  constant  pressure  and  a  current 
varying  with  the  number  of  lamps.  In  arc  work  we 
have  small  currents  and  often  very  high  pressures.  In 
incandescent  work  we  have  low  pressures  and  often 
enormous  currents.  Naturally  enough,  our  automatic 
protecting  devices  on  arc  systems  protect  against  ex- 
cesses of  pressure,  and  on  incandescent  systems  against 
excesses  of  current.  The  current  on  the  arc  system 
and  the  pressure  on  the  incandescent  system  are  regu- 
lated at  the  dynamo.  We  can  always  keep  ourselves 
from  confusing  the  two  systems  by  remembering  that 
an  arc  is  a  constant  current,  and  an  incandescent  a  con- 
stant pressure  system.  To  cut  off  a  lamp  on  a  series 
system,  we  shunt  the  current  around  the  lamp  with  a 
switch.  In  a  multiple  arc  system  we  cut  off  the  lamp 


LOW    POTENTIAL    SYSTEMS.  7 1 

by  disconnecting  it  from  the  circuit,  /.  e.,  by  introduc- 
ing an  opening  into  one  or  both  conductors  leading  to 
the  lamp.  In  each  system  the  cut-out  performs  the 
same  function  as  a  switch.  It  cuts  out  an  arc  lamp  by 
shunting  around  the  lamp,  and  an  incandescent  system 
by  opening  the  circuit  to  the  lamp. 

The  cut-out  in  an  arc  system  is  a  part  of  the  lamp 
itself,  and  its  design  need  not  be  considered  here.  In 
incandescent  systems,  however,  the  cut-outs  are  sep- 
arate devices,  and  they  are  of  the  kind  known  as  "fus- 
ible cut-outs."  There  are  many  kinds  of  these  cut-outs, 
some  good  and  some  very  bad.  Some  forms  have  been 
used  which  were  so  poor  in  design  that  they  themselves 
created  a  hazard.  It  is,  therefore,  of  the  utmost  impor- 
tance that  we  shall  thoroughly  understand  the  principle 
of  the  fusible  cut-out  and  what  distinguishes  a  good 
one  from  a  poor  one.  As  we  have  already  seen,  the 
passage  of  a  current  through  a  wire  heats  the  wire.  If 
the  current  is  strong  and  the  wire  is  of  small  diameter, 
the  wire  will  get  very  hot.  It  is  the  function  of  the  fus- 
ible cut-out  to  prevent  the  wire  of  a  circuit  from  receiv- 
ing a  current  strong  enough  to  overheat  it.  This  is 
accomplished  by  inserting  into  the  circuit  a  short  piece 
of  comparatively  fine  wire  (usually  of  some  material 
which  will  melt  at  a  low  temperature),  so  that  an  excess 
of  current  will  melt  or  "  fuse  "  this  piece  of  wire  before 
it  has  time  to  heat  the  circuit  wire  or  conductor  to  a 
temperature  that  could  ignite  inflammable  material  or 
even  injure  the  insulating  covering  of  the  conductor.  A 
device  by  which  such  a  fusible  wire  is  inserted  into  one 
or  both  wires  of  a  circuit  is  called  a  "  fusible  cut-out." 


72  THE    NATIONAL    ELECTRICAL    CODE. 

When  the  device  inserts  a  fusible  wire  or  "fuse"  into 
both  wires  of  a  circuit,  it  is  called  a  "double-pole"  cut- 
out, just  as  a  switch  which  opens  both  wires,  is  called  a 
double-pole  switch.  In  order  that  a  fusible  cut-out 
may  protect  a  circuit  to  a  lamp  or  a  group  of  lamps,  it 
must  be  so  placed  that  no  current  can  flow  to  the  cir- 
cuit except  through  the  cut-out.  If  of  correct  design 
and  size,  it  will  then  protect  all  conductors  beyond  it. 
The  code  devotes  considerable  space  to  statements  as  to' 
how  cut-outs  must  be  designed  and  installed.  A  fusible 
cut-out  only  protects  the  conductors  beyond  it,  so  that 
if  we  wish  to  protect  all  the  wires  in  a  building  from 
any  excessive  flow  of  current  from  the  outside,  we  must 
place  a  cut-out  as  near  as  possible  to  the  point  where 
the  conductors  enter  the  building,  as  specified  in  Rule 
15,  section  "b." 


CHAPTER    VIII. 

CLASS    C,     LOW    POTENTIAL    SYSTEMS.         PART    II. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  16.  UNDER- 
GROUND CONDUCTORS: — a.  Must  be  protected  against  moisture 
and  mechanical  injury,  and  be  removed  at  least  two  feet  from 
combustible  material  when  brought  into  a  building,  but  not  con- 
nected with  the  interior  conductors,  b.  Must  have  a  switch  and 
a  cut-out  for  each  wire  between  the  underground  conductors  and 
the  interior  wiring  when  the  two  parts  of  the  wiring  are  connected. 
These  switches  and  fuses  must  be  placed  as  near  as  possible  to  the 
end  of  the  underground  conduit,  and  connected  therewith  by  spe- 
cially insulated  conductors,  kept  apart  not  less  than  two  and  one- 
half  inches.  (See  Definitions.)  c.  Must  not  be  so  arranged  as  to 
shunt  the  current  through  a  building  around  any  catch-box. 

INSIDE  WIRING.  GENERAL  RULES: — 17.  At  the  entrance  of 
every  building  there  shall  be  an  approved  switch  placed  in  the 
service  conductors  by  which  the  current  may  be  entirely  cut  off. 
(See  Definitions.) 

18.  CONDUCTORS: — a.  Must  have  an  approved  insulating 
covering,  and  must  not  be  of  sizes  smaller  than  No.  14  B.  &  S., 
No.  16  B.  W.  G.(  or  No.  4  E.  S.  G.,  except  that  in  conduit 
installed  under  Rule  22,  No.  16  B.  &  S.,  No.  18  B.  W.  G.,  or  No. 
2  E.  S.  G.  may  be  used.  (See  Definitions.)  b.  Must  be  protected 
when  passing  through  FLOORS  ;  or  through  walls,  partitions,  tim- 
bers, etc. ,  in  places  liable  to  be  exposed  to  dampness  by  water- 
proof, non-c9mbustible,  insulating  tubes,  such  as  glass  or  porce- 
lain. Must  be  protected  when  passing  through  walls,  partitions, 
timbers,  etc. ,  in  places  not  liable  to  be  exposed  to  dampness  by 
approved  insulating  bushings  specially  made  for  the  purpose. 
(See  Definitions.)  c.  Must  be  kept  free  from  contact  with  gas, 

(73) 


74  THE    NATIONAL    ELECTRICAL   CODE. 

water  or  other  metallic  piping,  or  any  other  conductors  or  con- 
ducting material  which  they  may  cross  (except  high  potential  con- 
ductors) by  some  continuous  and  firmly  fixed  non-conductor 
creating  a  separation  of  at  least  one  inch  Deviations  from  this 
rule  may  sometimes  be  allowed  by  special  permission,  d.  Must 
be  so  placed  in  crossing  high  potential  conductors  that  there  shall 
be  a  space  of  at  least  one  foot  at  all  points  between  the  high  and 
low  tension  conductors,  e.  Must  be  so  placed  in  wet  places  that 
an  air  space  will  be  left  between  conductors  and  pipes  in  crossing, 
and  the  former  must  be  run  in  such  a  way  that  they  cannot  come 
in  contact  with  the  pipe  accidentally.  Wires  should  be  run  over 
all  pipes  upon  which  condensed  moisture  is  likely  to  gather,  or 
which  by  leaking  might  cause  trouble  on  a  circuit,  f.  Must  be  so 
spliced  or  joined  as  to  be  both  mechanically  and  electrically  secure 
without  solder.  They  must  then  be  soldered,  to  insure  preserva- 
tion, and  covered  with  an  insulation  equal  to  that  on  the  conduc- 
tors. (See  Definitions.) 

DEFINITIONS.  RULE  16.  UNDERGROUND  CONDUCTORS: — Sec- 
tion b.  The  cut-out  required  by  this  section  must  be  placed  so  as 
to  protect  the  switch.  RULE  17:— The  switch  required  by  this  rule 
to  be  approved  must  be  double  pole,  must  plainly  indicate 
whether  the  current  is  "on"  or  "off,  "and  must  comply  with 
sections  a,  c,  d  and  e  of  Rule  26  relating  to  switches.  RULE  18. 
CONDUCTORS: — Section  a.  In  so-called  "concealed"  wiring, 
moulding  and  conduit  work,  and  in  places  liable  to  be  exposed  to 
dampness,  the  insulating  covering  of  the  wire,  to  be  approved, 
must  be  solid,  at  least  g3?  of  an  inch  in  thickness,  and  covered 
with  a  substantial  braid.  It  must  not  readily  carry  fire,  must 
show  an  insulating  resistance  of  one  megohm  per  mile  after  two 
weeks'  submersion  in  water  at  70  degrees  Fahrenheit,  and  three 
days'  submersion  in  lime  water,  with  a  current  of  550  volts,  and 
after  three  minutes'  electrification.  For  work  which  is  entirely 
exposed  to  view  throughout  the  whole  interior  circuits,  and  not 
liable  to  be  exposed  to  dampness,  a  wire  with  an  insulating  cov- 
ering that  will  not  support  combustion,  will  resist  abrasion,  is  at 
least  ^  of  an  inch  in  thickness,  and  thoroughly  impregnated  with  a 
moisture  repellant,  will  be  approved.  Section  b,  second  para- 


LOW    POTENTIAL    SYSTEMS.  75 

graph.  Except  for  floors  and  for  places  liable  to  be  exposed  to 
dampness,  glass,  porcelain,  metal- sheathed  interior  conduit 
and  vulca  tube,  when  made  especially  for  bushings,  will  be 
approved.  The  tzvo  last  named  zvill  not  be  approved  if  cut 
from  the  usual  lengths  of  tube  made  for  conduit  zvork,  nor 
ivhen  made  without  a  head  or  flange  on  one  end.  Section/". 
All  joints  must  be  soldered,  even  if  made  with  the  Mclntyre  or 
any  other  patent  splicing  device.  This  ruling  applies  to  joints 
and  splices  in  all  classes  of  wiring  covered  by  these  rules. 

Underground  Conductors. — Section  "a"  requires 
that  special  care  shall  be  taken  in  installing  wires  at 
points  where  they  enter  a  building.  We  have  already 
called  attention  to  the  fact  that  at  all  points  where  wires 
pass  through  walls  special  care  should  be  exercised.  It 
is  almost  impossible  to  maintain  the  same  standard  of 
insulation  in  a  large  system  of  out-door  conductors 
(especially  if  they  are  underground)  that  we  can  main- 
tain on  a  system  of  conductors  confined  to  one  build- 
ing. We  should,  therefore,  when  we  are  compelled  to 
bring  outside  conductors  into  a  building,  use  the  best 
of  materials  and  workmanship,  as  called  for  in  section 
"a, "and  we  should  locate  the  safety  devices  which 
separate  the  outside  from  the  inside  conductors,  as 
near  as  possible  to  the  point  where  the  outside  wires 
enter  the  building,  as  required  in  section  "b."  The 
safety  devices  required  in  all  cases  are  a  hand  switch 
and  an  automatic  cut-out.  These  devices  have  been 
described  in  a  preceding  chapter.  The  cut-out  is  to 
protect  the  inside  wiring  from  any  excess  of  current 
that  might  overheat  the  conductors,  and  the  switch 
is  for  the  purpose  of  disconnecting  the'  wiring  in 
the  building  from  the  street  conductors.  This  switch 
is  a  necessary  protection  for  use  in  case  of  a  fire  in  the 


76  THE    NATIONAL    ELECTRICAL    CODE. 

building  or  of  any  serious  trouble  with  the  inside  cir- 
cuits. Ordinarily  this  switch  is  seldom  or  never  used 
except  to  disconnect  the  inside  wiring  from  the  central 
station  conductors  for  the  purpose  of  testing  its  insula- 
tion. Such  a  switch  should  always  be  installed  if  only 
for  convenience  in  testing,  as  nothing  is  more  essential 
for  the  safe  and  proper  maintenance  of  any  system  of 
conductors  than  that  it  shall  be  installed  in  such  a  man- 
ner that  it  can  at  all  times  be  easily  and  quickly  tested. 
The  object  of  locating  the  switch  as  required  in  the  defi- 
nition under  section  "b"  is  apparent  when  we  consider 
that  a  central  station  is  a  source  of  electrical  energy  of 
such  a  capacity  that  it  can  for  a  short  time  send  out  an 
almost  unlimited  supply.  The  station  can  readily  put 
out  current  enough  to  destroy  any  switch  that  would  be 
used  in  a  building,  so  that  we  must  consider  the  switch 
as  a  part  of  the  inside  system  to  be  protected  by  our 
cut-out. 

Rule  "c"  refers  to  a  ''catch-box."  This  name  is 
applied  t«  an  underground  chamber  located  in  the  street 
and  containing  the  "  safety  catches  "  or  fuses  which 
protect  the  street  mains  from  an  excessive  current. 
These  catches  connect  the  various  sections  of  the  con- 
ductors. If  there  is  any  excessive  rush  of  current  to 
any  section  of  the  street  conductors  it  is  the  function  of 
these  "catches"  to  melt  and  interrupt  the  flow.  If, 
however,  there  is  a  shunt,  or  another  path  in  multiple 
with  the  catch,  this  path  may  take  so  much  of  the  cur- 
rent that  the  catch  will  not  melt;  and  even  if  it  does 
melt  the  current  will  not  be  interrupted  but  will  still 
flow  through  the  shunt  circuit.  If,  therefore,  the  wiring 


LOW    POTENTIAL    SYSTEMS.  77 

of  a  building  is  so  installed  that  it  is  connected  as  a 
shunt  around  such  safety  catches,  this  wiring  may  at 
any  time  receive  an  unknown  amount  of  current,  regard- 
less of  the  number  of  lamps  or  motors  that  may  be  con- 
nected to  it.  While  the  inside  wiring  should  be  pro- 
tected from  damage  by  the  switches  and  cut-outs  above 
referred  to,  still  such  an  arrangement  of  circuits  ought 
never  to  be  allowed,  as  it  will  create  an  extraordinary 
hazard,  if  the  safety  devices  are  not  absolutely  certain 
in  their  action,  and  moreover  such  an  arrangement  is 
absolutely  needless.  It  could  never  be  of  any  advant- 
age and  would  be  an  annoyance  even  if  it  were  not  a 
source  of  danger. 

Inside  Wiring.  General  Rules. — The  switch  referred 
to  in  this  section,  is  the  same  device  that  is  required  by 
Rule  1 6.  The  design  of  the  switch  depends  upon  the 
system  used  and  upon  the  number  of  amperes  that  it  has 
to  carry.  The  essential  points  of  its  design  are  described 
under  Rule  26. 

Conductors.  — '  'Approved"  insulation  is  described  by 
the  definition  in  the  code.  The  list  of  wires  referred  to 
is  a  list  of  the  best  makes  of  wires  having  what  is 
known  as  a  moisture  proof  insulation.  This  insulation 
is  made  of  a  composition  of  which  the  chief  ingredient 
is  supposed  to  be  pure  rubber.  The  insulations,  how- 
ever, vary  greatly  in  composition,  and  the  fact  that  a 
wire  is  in  the  list  of  "approved  "  wires  in  the  code,  is 
no  guarantee  that  its  insulation  will  prove  satisfactory 
under  all  the  conditions  to  which  a  conductor  may  be 
subjected.  Some  of  the  wires  specified  are  of  a  much 
higher  grade  than  others.  A  wire  which,  under  ordi- 


78  THE    NATIONAL    ELECTRICAL    CODE. 

nary  circumstances,  will  hold  up  its  insulation  all  right, 
may  under  some  conditions  prove  worthless;  and 
another  wire  which  will  hold  up  under  these  conditions, 
may  prove  worthless  under  unfavorable  conditions  of 
another  kind.  We  must  always  select  our  insulation 
according  to  the  conditions.  In  selecting  a  wire  we 
must  consider  the  manner  in  which  it  is  to  be  installed 
and  the  agents  by  which  its  insulation  may  be  attacked, 
/'.  e. ,  whether  or  not  it  is  to  be  exposed  to  extreme  heat 
or  to  contact  with  oils  or  chemicals;  and  if  there  is  a 
probability  of  exposure  to  chemical  action  we  should 
consider  the  nature  of  the  chemicals  as  the  same  chem- 
icals act  quite  differently  upon  different  insulating  sub- 
stances. In  case  of  doubt  we  should  use  the  wire  which 
we  find  has  given  the  best  results  in  general  use,  and 
which  has  stood  the  test  of  time. 

As  regards  the  size  of  wires  to  be  used,  this  is  deter- 
mined as  far  as  safety  is  concerned,  by  the  table 
of  "safe  carrying  capacities,"  given  later  in  the  code. 

Wires  are  commonly  measured  in  one  of  the  follow- 
ing gauges:  Brown  and  Sharp,  Birmingham  Wire 
Gauge  or  Edison  Standard  Gauge.  The  abbreviations 
are  used  in  the  code.  The  code  allows  the  use  of  no 
wire  smaller  than  No.  146.  &  S.  gauge  or  its  equiva- 
lent in  other  gauges  (except  in  special  cases).  While  a 
number  16  B.  &  S.  wire  will  carry  6  amperes  more 
safely  than  a  number  14  will  carry  12  amperes  as  far  as 
overheating  is  concerned,  still  it  is  not  good  practice  to 
ever  use  a  wire  smaller  than  number  14  B.  &  S.  gauge 
in  any  place  where  it  can  be  subjected  to  a  mechanical 
strain.  A  wire  smaller  than  this  will  be  stretched  con- 


LOW    POTENTIAL    SYSTEMS.  79 

siderably  if  it  is  pulled  up  tight,  and  if  the  wire 
stretches,  the  insulation  must  also  stretch  and  thus 
become  subjected  to  a  permanent  strain.  Under  such 
a  strain,  any  insulation  must  eventually  give  way  and 
much  "  rubber  "  covering  will  soon  dry  out  and  become 
comparatively  brittle.  Again,  it  is  difficult  to  make  a 
good  twist  joint  in  a  very  small  wire  without  breaking 
or  cracking  the  wire,  especially  when  a  joint  is  made 
between  it  and  another  wire  of  a  larger  size.  It  is  very 
questionable  if  it  is  good  engineering  to  use  a  number 
1 6  B.  &  S.  wire  in  a  conduit.  The  only  place  where  it 
seems  excusable  to  use  a  small  wire  is  in  a  fixture 
carrying  a  few  lights  or  in  a  drop-cord  for  suspending 
one  light. 

The  requirements  of  section  "  b  "  call  for  an  extra 
insulation  at  what  we  have  found  to  be  the  weak  points 
of  a  system  of  inside  conductors.  The  tubes  or  bush- 
ings also  serve  as  a  mechanical  protection.  In  order  to 
carry  out  the  requirements  strictly  it  is  necessary  to  use 
insulating  bushings  at  all  points  where  wires  pass 
through  wood-work;  not  only  at  partitions  and  floors 
but  at  all  places  where  wires  are  run  through  holes  in 
timbers  or  studding.  Such  construction  not  only 
increases  the  insulation  but  also  allows  us  to  maintain 
a  pretty  good  insulation  even  if  the  insulating  cover- 
ing of  our  wire  deteriorates;  and  what  is  perhaps 
still  more  important,  it  prevents  the  wood-work  from 
becoming  charred  or  ignited  even  if  the  wires  become 
excessively  overheated.  If  glass  or  porcelain  tubes  are 
used  we  have  our  wire  installed  in  the  ideal  manner,  /'.  <?., 
we  have  it  treated  as  if  it  were  bare  wire. 


80  THE    NATIONAL    ELECTRICAL    CODE. 

At  the  present  price  of  porcelain  bushings,  it  is  no 
hardship  upon  the  owner  to  insist  upon  the  use  of 
moisture  and  fire-proof  bushings  for  all  holes  in  wood- 
work. As  to  what  places  are  "liable  to  be  exposed  to 
dampness,"  it  is  safe  to  assume  that  we  will  get  damp- 
ness at  any  place  where  there  are  wires  and  where  we 
do  not  want  it.  As  dampness  may  result  from  defective 
plumbing  or  any  accidental  overflow  of  water,  it  is  safe 
to  say  that  wires  in  any  building  with  water  pipes  in  it 
are  liable  to  be  exposed  to  dampness.  The  "Interior 
Conduit "  referred  to  in  the  definition  is  the  trade  name 
of  a  tubing  made  of  paper,  impregnated  with  a  water- 
proof compound.  "  Vulca  Duct "  is  the  trade  name  of 
another  tubing;  the  material  of  which  it  is  made  is  kept 
a  secret,  but  it  is  non-inflammable,  and  in  appearance 
resembles  hard  rubber,  for  which  it  is  used  as  a  substi- 
tute on  account  of  its  price,  which  is  very  much  less. 

Section  "c"  requires  a  mechanical  separation  of 
conductors  from  pipes  or  metallic  material.  While  an 
inch  of  air  is  almost  infinitely  better  insulation  than 
the  same  thickness  of  any  other  material  still  it  is 
impossible  to  be  certain  of  maintaining  an  air  gap 
between  a  wire  and  a  neighboring  pipe,  as  bc.th  pipes 
and  wire  are  liable  to  sag  or  to  get  displaced.  The 
safest  kind  of  construction  is,  therefore,  to  use  a  solid 
and  rigidly  fixed  separator,  so  that  we  may  be  sure  of 
preventing  any  metallic  contact  with  our  conductor. 
This  regulation  is  in  line  with  the  best  practice  con- 
cerning insulation  for  moderate  pressures,  which  is  to 
insist  not  so  much  upon  a  ridiculously  high  insulation 
on  new  work  as  upon  a  kind  of  construction  which  will 


LOW    POTENTIAL    SYSTEMS.  8 1 

permanently  maintain  an  insulation  which  is  high 
enough  to  insure  safety. 

The  extreme  care  required  by  section  "  d  "  is  neces- 
sitated, first,  by  the  fact  that  devices  attached  to  low 
potential  circuits  are  handled  by  every  one,  and  any 
contact  of  a  low  potential  wire  with  one  of  high  poten- 
tial may  bring  the  low  potential  circuit,  or  any  device 
connected  to  it,  up  to  the  potential  of  the  high  poten- 
tial circuit.  In  this  way  an  ordinarily  harmless  contact 
may  prove  fatal  to  human  life.  Secondly,  the  devices 
used  to  protect  a  low  pressure  system  are  not  suitable 
to  protect  it  when  subjected  to  an  abnormally  high 
pressure.  Thirdly,  the  insulation  which  may  be  all 
right  for  a  low  potential  system,  may  be  strained  and 
broken  down  by  the  high  pressure,  and  when  once  the 
insulation  has  given  way,  the  lower  pressure  keeps  up 
the  trouble  which  the  higher  pressure  has  started.  The 
perfect  insulation  of  wires  of  low  potential  from  those 
of  high  potential  is  therefore  even  more  important  than 
the  insulation  of  high  potential  wires  from  one  another 
or  from  the  ground. 

Section  "e"  requires  that  in  wet  places  there  shall 
be  not  only  a  solid  separator,  but  also  an  air  separation. 
While  almost  any  mechanical  separation  may  do  fairly 
well  between  wires  and  gas  pipes,  we  must  guard  against 
using  a  material  which  will  absorb  moisture  whenever 
we  have  a  water  pipe  near  our  wire.  A  piece  of  tubing 
strung  upon  the  wire  or  a  split  tube  placed  around  the 
pipe  and  held  in  place  by  adhesive  tape,  or  some  such 
simple  device,  easily  gives  the  desired  construction  and 
with  but  little  labor  or  expense. 

6 


82  THE    NATIONAL    ELECTRICAL    CODE. 

The  first  part  of  section  "f  "  may  be  described  as  a 
precaution  against  poor  workmanship.  It  requires  that 
the  wires  must  be  joined  mechanically  to  guard  against 
poor  soldering,  and  that  they  shall  be  soldered  to  guard 
against  poor  splicing.  The  solder  is  also  necessary 
even  if  the  joint  is  mechanically  perfect,  as  even  a  good 
twist  joint  will  in  time  deteriorate.  The  wire  will 
oxydize,  and  the  resistance  of  the  joint  will  increase. 
This  cannot  be  allowed,  as  any  resistance  in  a  circuit 
causes  energy  to  be  transformed  into  heat.  The 
soldering  of  the  joint,  if  properly  done,  insures  a 
good,  permanent  joint.  The  definition  under  section 
"f"  has  already  been  referred  to  in  the  paper  on 
high  potential  circuits. 

The  code  neglects  to  give  a  definition  of  how  to 
cover  a  joint  with  an  insulation  "equal  to  that  of  the 
conductors. "  We  know  of  no  way  in  which  this  can  be 
done  by  a  wireman,  but  the  rule  is  useful,  for  it  cer- 
tainly indicates  that  the  insulation  of  joints  must  be  as 
good  as  can  be  made,  and  it  directs  our  attention  to 
the  fact  that  joints  should  be  avoided  as  far  as  is  possi- 
ble. The  best  rule  to  observe  in  doing  work  is  to  avoid 
if  possible  the  use  of  any  joints  in  wires  except  where 
the  joints  come  in  the  air  between  supports.  The 
observance  of  this  rule  will  call  for  the  use  of  but  little 
more  wire  than  would  be  used  if  frequent  joints  were 
allowed.  When  we  consider  the  time  required  to  make 
a  really  first-class  joint  in  insulation,  and  the  time  lost 
in  making  over  joints  which  show  up  defective  on  being 
tested,  we  will  see  that  this  kind  of  construction  saves 
considerable  labor.  It  is  safe  to  say  that  doing  wiring 


LOW  POTENTIAL  SYSTEMS.  83 

without  joints  saves  as  much  in  labor  as  is  lost  in  mate- 
rial, and  this  is  the  only  way  that  we  can  be  certain  of 
securing  good  insulation. 


CHAPTER  IX. 

CLASS  C,  LOW  POTENTIAL  SYSTEMS.   PART  III. 

TEXT  OF  CODE  COVERED  BY  THIS  CHAPTER.  SPECIAL  RULES. 
19.  WIRING  NOT  ENCASED  IN  MOULDING  OR  APPROVED  CONDUIT: — 
a.  Must  be  supported  wholly  on  non-combustible  insulators,  con- 
structed so  as  to  prevent  the  insulating  coverings  of  the  wire  from 
coming  in  contact  with  other  substances  than  the  insulating  sup- 
ports, b.  Must  be  so  arranged  that  wires  of  opposite  polarity, 
with  a  difference  of  potential  of  150  volts  or  less,  will  be  kept 
apart  at  least  two  and  one-half  inches,  c.  Must  have  the  above 
distance  increased  proportionately  where  a  higher  voltage  is  used. 
d.  Must  not  be  laid  in  plaster,  cement  or  similar  finish,  e.  Must 
never  be  fastened  with  staples. 

IN  UNFINISHED  LOFTS"  BETWEEN  FLOORS  AND  CEILINGS,  IN 
PARTITIONS  AND  OTHER  CONCEALED  PLACES:—/".  Must  have  at 
least  one  inch  clear  air  space  surrounding  them.  g.  Must  be  at 
least  ten  inches  apart  when  possible,  and  should  be  run  singly  on 
separate  timbers  or  studding,  h.  Wires  run  as  above  immedi- 
ately under  roofs,  in  proximity  to  water-tanks  or  pipes,  will  be 
considered  as  exposed  to  moisture.  /'.  When  from  the  nature  of 
the  case  it  is  impossible  to  place  concealed  wire  on  non-combusti- 
ble insulating  supports  of  glass  or  porcelain,  the  wires  may  be 
fished  on  the  loop  system,  if  encased  throughout  in  approved 
continuous  flexible  tubing  or  conduit,  j.  Wires  must  not  be 
fished  for  any  great  distance,  and  only  in  places  where  the 
inspector  can  satisfy  himself  that  the  above  rules  have  been  com- 
plied with,  k.  Twin  wires  must  never  be  employed  in  this  class 
of  concealed  work. 

Before  considering  "special  rules"  for  wiring,  we 
will  first  consider  all  the  ways  in  which  it  has  been 

(84) 


LOW    POTENTIAL    SYSTEMS.  85 

customary  to  run  wires,  and  then  what  methods  are 
allowed  and  what  methods  are  recommended  by  the 
code.  Wires  are  in  general  run  in  two  ways:  First,  in 
accessible  places,  as  upon  the  walls  and  ceilings  of 
rooms;  second,  in  inaccessible  places,  as  in  walls,  and 
in  the  hollow  spaces  in  partitions  and  between  floors 
and  ceilings.  It  has  in  the  past  been  customary  to  run 
wires  in  all  of  the  following  ways:  In  accessible  places: 

(1)  The  wires  were  fastened   directly  upon   the   walls 
and  ceilings,  usually  by  means   of  wooden  cleats,    but 
sometimes  by  iron  staples.    (2;  The  wires  were  attached 
to  knobs  of  porcelain  or  glass  or  to  cleats  of  porcelain 
which  were  attached  to  the  walls  or  ceilings,  and  were 
so  designed  as  to  support  the  wires  in  the  air,  free  from 
the  wood  work  or  anything  but  the  insulating  supports. 
These  two  methods  of  construction  are  known  as  "open 
wiring."      (3)  The  wires   were    placed   in    grooves  in 
wooden  moulding  which  was  attached  to  the  ceilings  or 
walls.     (4)  The  wires  were  drawn  into  tubes  or  "  con- 
duits," the  conduits  being   attached   to  the  walls  and 
ceilings  by  means  of   staples  or  cleats.      In  inaccessible 
places:     (i)  Wires   attached  directly  to  walls   and  ceil- 
ings  and   concealed   by  being  covered  with  plaster  or 
cement.      (2)  Wires  run  in  hollow  spaces,  as  in  parti- 
tions and  between  floors  and  ceilings.      Both  of  these 
methods  were   known   as  "concealed  wiring."     When 
wires  were  concealed  by  running  them  in  hollow  spaces 
they  were   run  in   the   following   ways:   (i)  They  were 
"fished,"  i.  <?.,  they  were  drawn  into  the  space  through 
one  hole  and  drawn  out  of  the  space  through  another. 

(2)  They  were  run  directly  upon  the  woo d^ work  (where 


86  THE    NATIONAL    ELECTRICAL    CODE. 

wooden  construction  was  used),  the  wires  being  held  in 
place  by  cleats  or  staples  or  by  being  drawn  through 
holes  bored  in  timbers  or  joists.  (3)  The  wires  were 
occasionally  placed  in  moulding,  the  wires  and  mould- 
ing being  both  concealed.  (4)  The  wires  were  run 
upon  glass  or  porcelain  knobs  or  porcelain  cleats,  in 
the  same  manner  as  when  run  in  accessible  places,  the 
wires  being  surrounded  by  porcelain  bushings  where 
they  pass  through  timbers,  joists,  etc.  (5)  The  wires 
were  drawn  into  tubes  or  conduits,  the  conduits  being 
put  in  place  while  the  building  was  under  process  of 
construction,  and  the  wires  being  subsequently  drawn 
into  them.  We  have  spoken  of  the  various  ways  in 
which  wires  have  been  run,  as  some  of  these  methods, 
though  quite  popular  in  the  past  (on  account  of  the 
ease  and  cheapness  with  which  they  could  be  applied), 
are  now  absolutely  prohibited  by  the  code. 

Let  us  see  how  the  code  treats  of  the  various  methods 
of  construction  above  enumerated.  In  accessible  places: 
The  cleating  or  stapling  of  wires  upon  walls  or  ceilings 
is  forbidden  by  section  "  a  "  of  Rule  19.  The  running 
of  wires  upon  glass  or  porcelain  knobs  or  porcelain 
cleats  with  porcelain  or  glass  bushings  where  the  wires 
pass  through  floors  and  partitions  is  approved  by  sec- 
tions "a,"  "b"  and  "c"  of  Rule  19.  In  fact,  these 
sections  absolutely  compel  the  use  of  this  class  of  con- 
struction except  when  wires  are  enclosed  in  moulding 
or  conduits.  The  method  of  running  wires  in  moulding 
and  conduit  are  considered  at  length  in  a  later  portion 
of  the  code.  These  methods  are  approved  by  the  code. 
We  will,  devote  a  future  chapter  or  chapters  to  the 


LOW    POTENTIAL    SYSTEMS.  87 

discussion  of  these  systems.  In  inaccessible  places:  The 
concealing  of  wires  by  laying  them  in  plaster  or  cement 
is  specifically  forbidden  by  section  "  d  "  of  Rule  19. 
The  reason  for  this  requirement  is  that  wires  laid  in 
plaster  or  cement  are  exposed  to  chemical  actions 
which  often  destroy  the  waterproofing  qualities  of  their 
insulating  coverings.  Partially  slacked  lime  in  plaster 
will  "burn"  the  braid  and  rubber  coverings  of  wires, 
and  many  kinds  of  plasters  and  cements,  and  even  the 
tiles  of  which  ceilings  and  partitions  are  constructed, 
contain  chemicals  which  (either  alone  or  in  combina- 
tion with  moisture)  will  injure  and  sometimes  com- 
pletely destroy  insulation.  Again,  it  is  almost  impos- 
sible to  repair  defects  in  insulation  laid  in  plaster.  It 
is  practically  impossible  to  get  a  workman  to  make  a 
joint  in  insulation  that  is  water-tight  so  that  it  wilUnot 
leak  when  placed  in  wet  plaster.  The  consequence  is 
that  when  we  get  a  defect  in  the 'insulation  of  a  wire 
laid  in  plaster,  the  only  way  to  be  sure  of  removing  it 
is  to  remove  the  entire  wire  and  replace  it  with  another. 
This  class  of  construction  was  for  several  years  used 
almost  exclusively  in  wiring  fire-proof  buildings,  but 
the  results  obtained  have  been  most  unsatisfactory. 

The  method  of  "fishing  "  wires  into  hollow  spaces 
was  introduced  into  the  art  in  the  earliest  days.  The 
first  plants  installed  were  for  the  most  part  in  old  (i.  e., 
in  finished)  buildings,  where  hollow  spaces  were  inac- 
cessible. The  only  way  then  known  to  conceal  wire  in 
such  buildings  was  to  fish  it  into  hollow  spaces.  It  was 
fishing  in  a  very  literal  sense.  To  get  a  wire  from  one 
point  to  another,  the  wireman  would  bore  a  hole  in  the 


88  THE    NATIONAL    ELECTRICAL    CODE. 

wall  or  cut  a  small  hole  in  the  floor  and  then  push  a 
wire  into  the  hole  ;  then  either  he  or  another  man 
would  go  to  another  hole,  where  it  was  desired  to  have 
the  wire  come  out  of  the  wall  or  floor,  and,  taking  a 
piece  of  wire  with  the  end  bent  up  into  a  hook,  he 
would  fish  until  he  had  captured  the  loose  end  of  the 
wire.  Then  he  would  drag  the  wire  out  of  its  hole  and 
connect  the  end  to  his  socket  or  switch,  or  perhaps 
start  in  again  and  fish  to  another  hole.  With  this  kind 
of  work  it  was  of  course  utterly  impossible  to  know  the 
condition  or  position  of  wire  between  the  outlets. 
Wires  might  lie  against  pipes  or  be  crossed  and  tangled 
up  with  one  another  without  anyone  being  the  wiser. 
Defective  joints  could  not  be  discovered,  and,  in  fact, 
no  defective  workmanship  or  material  was  likely  to  be 
discovered  until  it  made  trouble.  It  was  so  easy  to 
rush  in  work  of  this  kind  and  still  have  it  pass  inspec- 
tion, when  first  installed,  that  many  a  man  who  wanted 
to  skin  the  cost  of  a  piece  of  work  would  even  run  a 
wire  of  inferior  insulation  inside  a  wall  and  tap  on 
some  ends  of  good  rubber-covered  wire  to  stick  through 
the  wall.  This  kind  of  construction  has  at  last  been 
condemned  by  the  underwriters,  and  section  "f"  of 
Rule  19  demands  a  grade  of  work  which  cannot  be 
obtained  by  "fishing." 

The  method  of  running  wires  upon  wood-work,  attach- 
ing them  with  cleats  or  staples  and  running  them 
through  holes  in  the  wood,  is  also  prohibited  by  section 
"f  "  and  by  section  "a."  This  kind  of  work,  once  so 
popular,  is  now  prohibited  in  accessible  places,  and  it 
goes  without  saying  that  its  use  in  concealed  work 
should  never  be  considered. 


LOW    POTENTIAL    SYSTEMS.  89 

The  use  of  moulding  in  concealed  work  is  prohibited 
by  the  code  in  the  portion  devoted  especially  to  mould- 
ings. 

The  method  of  running  wire  in  hollow  spaces  upon 
glass  or  porcelain  knobs  or  porcelain  cleats,  with  glass 
or  porcelain  tubes  surrounding  the  wires  where  they 
pass  through  timbers,  is  approved  by  the  code.  This 
class  of  construction  must  be  used  to  fulfill  the  require- 
ments of  sections  "f,"  "g"  and  "h"  of  Rule  19.  If 
the  wire  is  not  disturbed  after  it  has  once  been  installed, 
this  kind  of  construction  will,  if  properly  done,  secure 
almost  absolute  safety.  This  is  the  same  grade  of  work 
that  we  have  found  to  be  satisfactory  for  high  potential 
circuits.  The  wire  in  this  manner  would  have  an  insu- 
lation good  enough  to  secure  safety  even  if  it  did  not 
have  a  rubber  covering.  In  fact  if  we  could  be  assured 
that  the  wire  run  in  this  manner  would  never  be  molested 
after  it  had  once  been  properly  installed,  we  could  use 
a  bare  wire  without  necessarily  creating  a  hazard.  Of 
course  the  use  of  good  construction  is  no  excuse  for 
the  use  of  inferior  material. 

The  best  practice  is  to  use  a  high  grade  of  insulated 
wire  and  to  install  it  if  possible  in  such  a  way  that  it 
would  not  create  a  hazard  even  if  its  insulation  were 
injured  or  destroyed. 

The  last  method  mentioned,  *.  e.,  the  running  of 
wires  in  conduit,  is  approved  by  the  code.  Consider- 
able space  is  given,  in  another  part  of  the  code,  to  the 
manner  in  which  the  conduit  should  be  installed  and  we 
propose  to  devote  one  or  more  chapters  to  the  subject 
of  conduits  when  we  come  to  that  part  of  the  code.  In 


90  THE    NATIONAL    ELECTRICAL    CODE. 

summing  up  what  we  have  stated  above  concerning 
methods  of  wiring  and  the  code,  we  find  that  the  follow- 
ing methods  are  approved  by  the  code  and  that  they 
are  the  only  methods  allowed:  (i)  Wires  run  on  glass  or 
porcelain  knobs  or  cleats,  (with  bushings  of  same  mate- 
rials) either  for  "open"  or  "concealed"  work.  (2) 
Wires  run  in  a  suitable  wooden  moulding,  (but  not  con- 
cealed work).  (3)  Wires  run  in  a  suitable  conduit  for 
either  open  or  concealed  work. 

Sections  " i, "  "  j  "  and  "  k  "  of  Rule  1 9  permit  the  use 
of  a  special  kind  of  construction,  in  cases  where  it  is 
practically  impossible  to  install  the  work  in  the  manner 
which  is  considered  the  best.  This  exception  is  made 
to  provide  a  method  by  which  the  wires  can  be  run  con- 
cealed \\\.  finished  buildings.  The  code  requires  that  con- 
duits for  interior  conductors  shall  be  of  material  which 
is  "not  subject  to  mechanical  injury  by  saws,  chisels  or 
nails,"  but  as  there  is  no  flexible  conduit  on  the  market 
which  fills  this  specification,  a  conduit  is  allowed,  for 
this  particular  class  of  work,  which  is  not  tool  proof. 
This  kind  of  construction  is  infinitely  better  than  the  old 
practice  of  fishing  the  wires,  and  it  is  not  liable  to  cre- 
ate a  hazard,  as  there  is  comparatively  little  danger  of 
mechanical  injury  to  a  conduit  in  a  finished  building, 
particularly  in  cases  where  it  is  not  allowable  to  cut  up 
the  building  enough  to  insert  a  standard  conduit. 


CHAPTER    X. 

CLASS    C. ,     LOW    POTENTIAL    SYSTEMS.        PART    IV. 

TEXT  OF  CODE  COVERED  BY  THIS  CHAPTER.  20.  MOULDINGS:— 
a.  Must  never  be  used  in  concealed  work  or  in  damp  places,  b. 
Must  have  at  least  two  coats  of  water-proof  paint  or  be  impreg- 
nated with  a  moisture  repellant.  c.  Must  be  made  of  two  pieces, 
a  backing  and  capping,  so  constructed  as  to  thoroughly  incase 
the  wire  and  maintain  a  distance  of  one-half  inch  between  con- 
ductors of  opposite  polarity  and  afford  suitable  protection  from 
abrasion. 

21.  SPECIAL  WIRING: — In  breweries,  packing-houses,  stables, 
dye-houses,  paper  and  pulp  mills,  or  other  buildings  specially 
liable  to  moisture  or  acid,  or  other  fumes  liable  to  injure  the 
wires  or  insulation,  except  where  used  for  pendants,  conductors: 
a.  Must  be  separated  at  least  six  inches,  b.  Must  be  provided 
with  an  approved  water-proof  covering.  (See  Definitions.)  c. 
Must  be  carefully  put  up.  d.  Must  be  supported  by  glass  or  por- 
celain insulators.  No  switches  or  fusible  cut-outs  will  be  allowed 
where  exposed  to  inflammable  gases  or  dust,  or  to  flyings  of  com- 
bustible material,  e.  Must  be  protected  when  passing  through 
floors,  walls,  partitions,  timbers,  etc.,  by  water-proof,  non-com- 
bustible, insulating  tubes,  such  as  glass  or  porcelain. 

DEFINITIONS.  RULE  21.  SPECIAL  WIRING: — Section  b.  The 
insulating  covering  of  the  wire  to  be  approved  under  this  section 
must  be  solid,  at  least  g±  of  an  inch  in  thickness  and  covered  with 
a  substantial  braid.  It  must  not  readily  carry  fire,  must  show  an 
insulating  resistance  of  one  megohm  per  mile  after  two  weeks' 
submersion  in  water  at  70  degrees  Fahrenheit,  and  three  days' 
submersion  in  lime  water  with  a  current  of  550  volts  after  three 
minutes'  electrification,  and  must  also  withstand  a  satisfactory 


92  THE    NATIONAL    ELECTRICAL    CODE: 

test  against  such  chemical  compounds  or  mixtures  as  it  will  be 
liable  to  be  subjected  to  in  the  risk  under  consideration. 

Moulding. — Section  "a,"  Rule  20,  limits  the  use  of 
moulding  to  dry  places  and  even  in  dry  places  it  is  only 
allowed  as  a  substitute  for  insulator  or  cleat  work.  We 
have  seen  that  the  first  thing  to  be  sought  is  accessibil- 
ity. Nothing  could  be  more  inaccessible  than  a  wire 
in  a  moulding  inside  a  partition  or  between  floors  and 
ceiling.  Again  we  have  seen  that  moisture  is  the  great- 
est foe  to  insulation.  It  is  not  therefore  permissible 
to  place  wires  in  damp  places  as  near  together  as  they 
are  placed  in  mouldings.  In  fact,  in  a  damp  place, 
wires  in  moulding  are  more  exposed  to  moisture  than 
wires  placed  near  to  one  another  in  the  air,  as  the 
wood  of  the  moulding  will  absorb  moisture  and  the 
wires  will  quickly  become  wet  but  will  dry  very  slowly. 
Section  "b"  of  the  same  rule  is  made  necessary  by 
the  well  known  tendency  of  wood  to  absorb  moisture 
even  in  a  place  which  is  not  supposed  to  be  wet.  In 
the  wiring  of  a  building  the  moulding  is  placed  against 
wet  plaster  or  cement  and  unless  some  precaution  is 
taken  to  prevent  the  wood  from  absorbing  moisture  the 
moulding  will  become  saturated  and  will  remain  wet 
after  almost  everything  else  in  the  building  has  become 
dry.  The  surface  of  the  wood  which  comes  in  contact 
with  the  plastered  wall  should  always  be  painted  or 
filled;  and  naturally  the  more  thoroughly  the  moulding 
is  made  waterproof  the  better.  Section  "c"  is  inserted 
in  Rule  20  to  prevent  the  practice  (almost  universal  in 
the  past)  of  placing  the  wires  against  a  wall  and  cov- 
ering them  with  a  grooved  moulding.  This  method 


LOW    POTENTIAL    SYSTEMS.  93 

was,  of  course,  cheaper  than  to  provide  wood  to  cover 
the  wire  and  also  to  keep  it  away  from  the  wall.  The 
trouble  with,  such  construction  was  that  the  wire  was 
placed  in  contact  with  the  plaster  while  it  was  new  and 
wet  and  that  the  rubber  compound  with  which  the  wires 
were  covered  was  liable  to  be  injured  by  the  action  of 
any  chemicals  that  might  enter  into  the  composition  of 
the  plaster.  The  moulding  which  is  required  by  the 
code,  must  be  so  made  that  it  separates  the  wires  half 
an  inch  from  each  other  and  also  covers  the  wires  so 
as  to  keep  them  in  place  and  at  the  same  time  protect 
them  from  any  ordinary  mechanical  injury 

The  only  practical  form  of  moulding  which  will 
do  these  things  is  a  moulding  made  of  two  pieces. 
There  are  many  forms  of  mouldings,  but  in  general  the 
piece  next  to  the  wall  is  called  the  backing  and  the 
piece  which  covers  the  wires  is  called  the  capping. 

We  have  spoken  of  moisture  as  being  the  greatest  foe 
of  insulation,  yet  pure  water  is  not  such  a  very  good 
conductor.  In  fact  it  is  a  very  poor  conductor  of  elec- 
tricity; but  water  which  holds  in  solution  any  foreign 
matter  either  an  acid  or  a  salt  is  a  pretty  good  conduc- 
tor. As  many  chemical  substances  act  directly  to 
destroy  the  rubber  compound  which  covers  our  wire, 
the  conditions  described  in  Rule  21  act  unfavorably  in 
two  ways;  first,  there  is  a  tendency  to  destroy  the  insu- 
lation, and  second,  the  chemicals  tend  to  furnish  a  good 
path  for  a  leak  after  the  insulating  material  has  been 
injured  or  destroyed.  By  "  pendants  "  are  meant  the 
wires  which  hang  down  and  from  which  the  lamp  sock- 
ets are  directly  suspended.  These  wires  cannot  well  be 


94  THE    NATIONAL    ELECTRICAL    CODE. 

kept  apart,  but  they  should  have  an  insulation  as  good 
as  that  of  any  other  parts  of  the  wiring.  Section  "  a  " 
of  Rule  21  requires  that  the  wires  shall  be  kept  six  inches 
apart  in  places  where  they  are  exposed  to  the  action  of 
chemicals.  This  is  equivalent  to  a  decision  that  it  is  as 
difficult  to  maintain  insulation  on  a  low  potential  sys- 
tem, where  the  wires  are  thus  exposed,  as  it  is  to  main- 
tain insulation  on  a  high  potential  system,  under  ordi- 
nary conditions.  In  reality  the  difficulty  is  greater; 
and  in  some  cases  it  is  almost  impossible  to  maintain  a 
high  insulation  with  any  kind  of  material  and  construc- 
tion. 

Section  "b"  calls  for  the  highest  grade  of  insulated 
wire.  The  life  of  the  insulation  on  a  wire  when  exposed 
to  chemical  action  is  usually  short.  The, best  insulation 
that  the  market  affords  is  none  too  good  for  this  class 
of  work  and  the  safe  thing  to  do  (and  the  cheapest  thing 
in  the  long  run)  is  to  buy  the  very  best  wire  that  can 
be  bought  for  use  in  places  such  as  are  described  in  this 
rule.  Even  if  we  do  this  we  cannot  be  sure  of  our 
results  unless  we  select  a  make  of  wire  which  has  a 
record  for  withstanding  the  action  of  the  particular 
chemicals  to  which  it  is  liable  to  be  exposed. 

The  simple  rule  laid  down  in  section  "c"  is  the 
most  important  of  any  to  be  observed.  Where  wires 
are  run  in  the  air  and  are  supported  upon  insulators, 
the  only  places  where  the  current  can  leak  from  one 
wire  to  another  or  from  a  wire  to  the  ground  is  at  the 
points  of  support.  If  a  wire  is  carelessly  put  up,  it  is 
liable  to  be  injured  at  these  very  points.  If  the  insula- 
tion becomes  broken,  then  no  matter  how  good  it  was 


LOW    POTENTIAL    SYSTEMS.  95 

originally,  our  wire  is  no  better  than  a  bare  wire.  If 
a  short  kink  is  made  in  a  wire  or  if  is  tied  too  tightly  to 
an  insulator,  a  permanent  strain  is  placed  upon  the  rub- 
ber insulation  and  its  life  may  be  reduced  to  a  small 
fraction  of  what  it  would  be  if  put  up  with  judgment 
and  care.  Only  skill  and  care  can  secure  work  that 
will  give  good  insulation  and  will  insure  safety  in  case 
the  insulated  covering  of  the  wire  is  injured. 

The  kind  of  construction  called  for  in  section  "d" 
is  required  by  the  code  in  dry  places  and  it  is  still  more 
imperative  that  it  shall  be  employed  in  wet  ones.  In 
dry  places  the  principal  virtue  of  our  glass  and  porce- 
lain is  that  they  are  fire  proof.  In  damp  places  how- 
ever and  especially  in  places  where  wires  are  exposed 
to  chemical  action  we  need  glass  or  porcelain  to  help 
us  maintain  insulation. 

In  this  connection,  we  should  notice  that  most  of  the 
porcelain  made  in  this  country  in  the  past  and  much  of 
the  porcelain  now  on  the  market,  is  almost  worthless  as 
far  as  insulation  is  concerned.  Only  a  few  years  ago 
we  were  compelled  to  use  glass  exclusively  for  use  in 
packing-houses  and  the  like,  owing  to  the  inferior  qual- 
ity of  the  porcelain  which  was  then  used  for  making 
insulators.  Inferior  porcelain  is  so  porous  that  it  will 
absorb  moisture  like  a  sponge,  so  that  all  the  insulation 
it  affords  is  that  of  the  thin  glaze  on  the  surface.  Since 
knobs  are  not  glazed  on  the  bottom,  a  porous  knob  on 
a  wet  wall  will  become  thoroughly  saturated  with  moist- 
ure, and  if  there  is  a  check  in  the  glaze,  the  knob  prac- 
tically ceases  to  be  an  insulator  at  all.  When  porcelain 
is  used  for  this  work  it  should  be  thoroughly  vitrified, 


96  THE    NATIONAL    ELECTRICAL    CODE. 

and  any  porcelain  which  is  not  thoroughly  vitrified 
should  be  condemned.  We  have  seen  that  when  a  cir- 
cuit carrying  a  current  is  opened,  an  arc  is  formed. 
This  is  just  what  we  get  when  a  circuit  is  opened  by  the 
opening  of  a  switch  or  the  blowing  of  a  fuse.  The 
danger  of  allowing  a  spark  to  be  made  in  the  presence 
of  inflammable  gases  or  of  fine  dust  is  too  well  under- 
stood by  all  insurance  men  to  need  any  comment.  By 
making  an  installation  in  accordance  with  the  spirit  of 
Rule  21  we  can  not  only  furnish  light  in  places  such  as 
are  described  in  section  "  d  "  (without  creating  a  haz- 
ard), but  a  light  which  is  safer  than  any  other  kind  of 
illuminant. 

The  code  requires  that  all  wires,  whether  of  high  or 
low  potential  systems,  shall  be  protected  wherever  they 
pass  through  walls  by  insulating  tubes.  For  high  poten- 
tial systems  and  for  the  class  of  work  referred  to  in 
Rule  21,  the  tubes  must  be  of  glass  or  porcelain  or 
some  other  incombustible  material.  Rule  18,  which  we 
have  considered  in  a  previous  chapter,  allows  the  use 
of  tubes  of  other  materials  on  low  potential  systems,  in 
places  where  wires  are  not  liable  to  be  exposed  to 
moisture;  but  as  almost  any  wall  or  partition  is  liable 
to  be  a  place  where  wires  are  exposed  to  moisture,  and, 
as  tubes  of  porcelain  are  at  present  quite  inexpensive, 
and  nearly  or  quite  as  cheap  as  the  other  bushings 
referred  to  in  Rule  18  and  the  definitions  explaining 
that  rule,  it  can  hardly  be  considered  good  practice  to 
run  wires  of  any  kind  through  walls  or  partitions  with- 
out protecting  them  in  the  manner  described  in  section 
"c"  of  Rule  21. 


CHAPTER   XI. 

CLASS    C,    LOW    POTENTIAL    SYSTEMS.        PART    V. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  22.  INTE- 
RIOR CONDUITS*: — (See  Definitions.)  a.  Must  be  continuous 
from  one  junction  box  or  another,  or  to  fixtures,  and  must  be  of 
material  that  will  resist  the  fusion  of  the  wire  or  wires  they  con- 
tain without  igniting  the  conduit,  b.  Must  not  be  of  such  mate- 
rial or  construction  that  the  insulation  of  the  conductors  will 
ultimately  be  injured  or  destroyed  by  the  elements  of  the  compo- 
sition, c.  Must  be  first  installed  as  a  complete  conduit  system, 
without  conductors,  strings,  or  anything  for  the  purpose  of  draw- 
ing in  the  conductors,  and  the  conductors  then  to  be  pushed  or 
fished  in.  The  conductors  must  not  be  placed  in  position  until 
all  mechanical  work  on  the  building  has  been,  as  far  as  possible, 
completed,  d.  Must  not  be  so  placed  as  to  be  subject  to  mechan- 
ical injury  by  saws,  chisels  or  nails,  c.  Must  not  be  supplied 
with  a  twin  conductor,  or  two  separate  conductors,  in  a  single 
tube.  (See  f  Rule  22.)  f.  Must  have  all  ends  closed  with  good 
adhesive  material,  either  at  junction  boxes  or  elsewhere,  whether 
such  ends  are  concealed  or  exposed,  [oints  must  be  made  air- 
tight and  moisture-proof,  g.  Conduits  must  extend  at  least  one 
inch  beyond  the  finished  surface  of  walls  or  ceilings  until  the 

*The  object  of  a  tube  or  conduit  is  to  facilitate  the  insertion  or  extraction  of 
the  conductors,  to  protect  them  from  mechanical  injury,  and,  as  far  as  possible 
from  moisture.  Tubes  or  conduits  are  to  be  considered  merely  as  raceways,  and 
are  not  to  be  relied  on  for  insulation  between  wire  and  wire,  or  between  the  wire 
and  the  ground. 

tNoTE. — The  use  of  two  Standard  wires,  either  separate  or  twin  conductor, 
in  a  straight  conduit  installation  is  approved  in  the  iron-armored  conduit  cr:  the 
Interior  Conduit  and  Installation  Company,  but  not  in  any  of  the  other  approved 
conduits.  (See  Rule  22,  <?.) 

7  (97) 


98  THE    NATIONAL    ELECTRICAL    CODE. 

mortar  or  other  similar  material  be  entirely  dry,  when  the  projec- 
tion may  be  reduced  to  half  an  inch. 

DEFINITIONS.  RULE  22.  INTERIOR  CONDUITS: — The  brass- 
sheathed  and  the  iron-armored  tubes  made  by  the  Interior  Con- 
duit and  Insulation  Company,  the  American  Circular  Loom  Co. 
tube  and  the  Vulca  tube  are  approved  for  the  class  of  work  called 
for  in  this  rule. 

Interior  Conduits, — We  have  already  called  special 
attention  to  the  fact  that  in  order  to  have  the  best  kind 
of  an  installation,  it  is  necessary  to  have  the  wires  at 
all  times  accessible.  Accessibility  may  be  obtained  in 
three  ways:  First,  by  running  wires  upon  knobs  or 
cleats,  the  wires  being  either  in  sight  upon  walls  or 
ceilings,  or  in  the  hollow  spaces,  as  in  attics,  unfinished 
rooms,  ventilating  shafts,  etc.,  or  in  runways  specially 
provided  for  the  purpose.  Second,  by  running  the 
wires  in  wooden  mouldings  so  constructed  that  we  can 
remove  the  covering  or  "capping"  and  inspect  the 
wires  or  remove  and  replace  them  in  case  of  injury  to 
the  insulation.  These  two  methods  suffice  to  secure 
good  insulation,  but  they  do  not,  except  in  special 
cases,  admit  of  construction  which  will  allow  the  wires 
to  be  concealed  from  view  and  at  the  same  time  pro- 
tected against  mechanical  injury.  The  third  method 
consists  of  running  the  wires  in  a  pipe  or  conduit  so 
constructed  that  the  wires  can  be  readily  withdrawn 
and  other  wires  drawn  in,  if  at  any  time  the  insulating 
covering  of  the  wires  is  injured.  This  system,  if  prop- 
erly installed,  allows  us  to  withdraw  the  wires  for 
inspection  and  to  readily  insert  them  again.  The  object 
of  the  interior  conduit  is  briefly  and  very  clearly  set 
forth  in  the  note  given  above  in  the  text  of  the  code. 


LOW    POTENTIAL    SYSTEMS.  99 

An  interior  conduit  can  often  be  used  to  good  advantage 
in  the  place  of  moulding,  but  its  tfoefuse  is  to  allow 
wires  to  be  "  concealed"  without  being  "fished."  To 
accomplish  this  result  a  conduit  should  fulfill  two  require- 
ments :  First,  it  should  prevent  the  igniting  of  wood- 
work, in  the  event  of  the  wires  becoming  overheated  by 
excess  of  current,  or  in  case  an  arc  is  set  up  either  by 
a  break  in  a  wire  carrying  a  current  or  by  wires  of 
opposite  polarity  becoming  "crossed,"  /.  e.,  coming 
into  electrical  contact  with  one  another  either  directly 
or  through  some  conducting  path.  Second,  it  should 
furnish  mechanical  protection  to  the  wires,  so  that  the 
insulating  covering  of  the  wires  will  not  be  mechan- 
ically injured  or  destroyed. 

The  interior  conduit,  like  everything  else  in  the  art, 
has  passed  through  a  period  of  evolution.  Although 
the  conduit  system  is  still  susceptible  of  improvement, 
it  is  to-day  so  well  developed  that  we  can  apply  it  suc- 
cessfully and  at  a  reasonable  cost  to  almost  all  classes 
of  concealed  work.  In  considering  the  advantages  and 
requirements  of  a  conduit,  we  must  consider  the  class 
of  construction  which  it  was  designed  to  replace.  It  is 
necessary  in  most  inside  wiring  for  incandescent  lamps 
to  have  our  wires  out  of  sight,  or,  as  we  commonly 
express  it,  "concealed."  Before  we  had  the  conduit, 
this  was  accomplished  in  three  ways  :  First,  the  wires 
were  run  on  insulators  or  cleats  upon  beams  and  rafters, 
in  the  hollow  spaces  in  walls,  partitions,  and  below 
floors.  Second,  they  were  fastened  with  staples  or 
cleats  directly  upon  ceilings  or  walls  and  covered  with 
plaster.  Third,  they  were  fished  into  the  hollow  spaces 


100  THE    NATIONAL    ELECTRICAL    CODE. 

in  partitions  or  between  ceilings  or  floors.  Whichever 
of  these  methods  was  employed,  the  wires  were  inacces- 
sible ;  they  were  liable  to  mechanical  injury  from  tools 
in  the  hands  of  plasterers,  carpenters,  plumbers,  gas 
fitters  and  the  like.  They  were  also  liable  to  be  injured 
by  chemical  action,  especially  when  laid  in  cement  or 
plaster.  Where  wire  is  laid  in  plaster,  in  modern  city 
buildings,  the  life  of  the  insulation  is  a  matter  of  com- 
plete uncertainty.  The  evolution  of  the  conduit  has 
brought  about  a  gradual  improvement  in  materials, 
appliances  and  methods  of  installation;  but  the  advance 
has  been  chiefly  in  the  matter  of  educating  people  to 
use  it.  Although  thoughtful  engineers  have  long  seen 
the  advantages  to  be  derived  by  running  wires  in  pro- 
tecting pipes,  it  seemed  as  if  the  additional  expense 
would  be  so  great  that  such  a  system  could  never  be 
successfully  introduced.  The  first  conduit  placed 
upon  the  market  was  called  "The  Interior  Conduit." 
The  tubing  was  formed  of  strips  of  paper  wound 
spirally  layer  upon  layer,  the  paper  being  saturated 
with  a  water-proof  compound.  The  tubes  were  joined 
at  the  ends  with  thin  brass  couplings  or  sleeves,  which 
were  slid  over  the  ends  of  both  tubes  and  crimped  so 
as  to  form  a  practically  water-tight  joint.  In  order  to 
get  the  conduit  into  use,  an  attempt  was  made  to  depend 
upon  the  conduit  itself  for  insulation.  It  was  thought 
necessary  to  do  this  in  order  to  make  conduit  construc- 
tion cheap  enough  to  be  extensively  used.  The  attempt 
was  made  to  save  enough  in  the  cost  of  insulating  cover- 
ing of  the  wires  to  pay  or  nearly  pay  for  the  tubing.  The 
result  of  this  experiment  was  disastrous  in  the  extreme. 


LOW    POTENTIAL    SYSTEMS.  IOI 

At  first  each  tube  contained  two  wires,  which  were 
insulated  only  by  a  wrapping  of  cotton.  The  idea  was 
that  the  wires  would  either  be  insulated  by  the  conduit 
itself,  or,  if  the  insulation  was  impaired,  the  wires 
would  come  into  metallic  connection  with  one  another, 
when  the  result  would  be  simply  that  the  protecting 
fuse  would  melt  and  protect  the  circuit.  New  wires 
would  then  be  drawn  into  the  conduit.  The  scheme 
worked  exactly  according  to  the  calculations,  but  it 
worked  so  well  that  the  wires  were  practically  crossed 
all  the  time.  The  next  step  was  to  use  two  conductors 
of  underwriters'  wire,  or  wire  covered  with  cotton  braid 
saturated  with  white  paint.  This  wire  .lasted  but  little 
better.  Next,  two  weather-proof  wires  were  used,  i.  e., 
wires  covered  with  cotton  braids  saturated  with  a  water- 
proof compound  (two  wires  were  placed  in  a  tube). 
This  wire  lasted  a  little  better,  but  soon  went  the  way 
of  the  others.  Next,  the  attempt  was  made  to  get  along 
with  moisture-proof  insulation  on  one  of  the  two  wires 
only.  One  conductor  was  covered  with  a  covering  of 
"rubber,"  and  the  second  wire  was  wound  spirally 
around  the  first,  outside  the  rubber  covering,  and  a 
weather-proof  braid  was  placed  around  the  outside. 
This  wire  lasted  fairly  well  where  the  conditions  were 
favorable,  but  was  not  satisfactory  for  general  use. 
The  next  step  was  to  use  a  similar  double  conductor, 
with  a  second  rubber  covering  around  the  outside  con- 
ductor, so  that  the  wires  were  insulated  from  one 
another  and  from  the  conduit  with  moisture-proof  insu- 
lation. Having  at  last  reached  the  point  where  the 
cost  was  practically  the  same  as  that  of  two  rubber- 


IO2  THE    NATIONAL    ELECTRICAL    CODE. 

covered  wires,  the  next  step  was  to  use  two  wires  with 
the  same  insulation  that  had  been  used  for  other  con- 
cealed work,  excepting  that  the  insulation  was  not  quite 
as  thick  as  was  used  for  wires  laid  in  plaster.  Having 
reached  the  point  where  the  advantages  of  a  conduit 
system  had  been  demonstrated,  and  having  learned  by 
experience  that  good  conduit  construction  must  be  more 
expensive  than  running  wires  fished  or  in  plaster,  the 
conduit  manufacturers  undertook  to  sell  conduit  on  its 
merits,  and  took  the  stand  that  the  extra  expense  of 
installation  was  justified  on  the  score  of  safety,  and 
that  in  the  long  run  the  owner  would  save  in  mainte- 
nance more  than  he  lost  in  the  first  cost.  Introduced 
along  these  lines,  the  interior  conduit  has  become  a 
success,  and  to-day  it  is  extensively  used  on  almost 
every  installation  where  a  high  grade  of  insulation  is 
desired,  and  its  use  is  rapidly  increasing.  After  the 
paper  tube,  another  form  of  conduit,  called  "  vulca 
duct,"  was  brought  out.  The  advantage  claimed  for 
this  conduit  is  that  it  is  absolutely  non-combustible. 
The  manufacturers  of  vulca  duct  early  recommended 
the  use  of  a  separate  tube  for  each  wire,  even  where 
small  wires,  carrying  the  current  of  a  few  lights,  were 
used.  The  next  step  was  to  place  a  mechanical  protec- 
tion in  the  form  of  a  metal  covering  around  the  conduit. 
At  first  this  was  a  covering  of  thin  sheet  brass,  but 
finally  it  took  the  form  of  a  substantial  iron  pipe.  At 
last  we  have  a  conduit  system  consisting  of  what  is 
practically  a  gas  pipe  with  an  -insulating  lining,  the  wire 
used  being  as  good  as  is  used  for  any  class  of  construc- 
tion. The  covering  of  the  wire  provides  the  insulation, 


LOW    POTENTIAL    SYSTEMS.  103 

the  tube  provides  the  required  accessibility,  and  where 
there  is  exposure  to  mechanical  injury,  the  metal  cov- 
ering is  used  to  furnish  mechanical  protection. 

Section  "a.  "  Rule  22  means  that  the  conduit  must  be 
continuous  between  outlets,  and  continuous  in  the  sense 
of  being  as  nearly  as  possible  equivalent  to  a  continuous 
water  and  air-tight  tube,  in  accordance  with  section  "  f. " 

Section  "  c  "  is  an  imperative  rule.  Only  by  instal- 
ling conduit  and  wire  in  this  manner  can  we  be  assured 
that  the  wires  will  be  accessible.  The  insertion  of 
wires  after  the  conduit  is  complete  in  place  is  the  best 
test  of  the  manner  in  which  the  conduit  has  been 
installed  and  it  is  the  only  way  in  which  a  concealed 
conduit  can  be  tested  after  it  is  once  installed  and 
hidden  from  view. 

Consideration  of  section  "  d  "  determines  the  kind  of 
conduit  best  suited  to  any  particular  piece  of  work. 
The  spirit  of  this  rule  requires  that,  in  most  cases 
where  tubes  are  run  in  unfinished  buildings,  wherever 
tubes  are  run  below 'floors  and  in  general  in  all  places 
where  the  conduit  is  liable  to  mechanical  injury  it 
should  be  "armored,"/,  e.,  there  should  be  a  metal 
covering  to  protect  the  wire  and  it  should  be  thick 
enough  to  turn  a  nail.  The  best  conduit  yet  devised 
for  mechanical  protection  is  an  ordinary  gas  pipe.  The 
"iron  armored"  conduit  of  the  Interior  Conduit  Com- 
pany, is  a  gas  pipe  lined  with  a  tube  of  paper  saturated 
with  a  water-proof  compound.  The  essential  parts  of  a 
conduit  are:  first,  a  hole  into  which  to  draw  the  wire; 
second,  the  protecting  covering  for  the  wire.  The  insu- 
lating lining  should  #0/be  depended  upon  for  insulation, 


104  THE    NATIONAL    ELECTRICAL    CODE. 

but  its  presence  is  approved  by  the  underwriters,  as  pro- 
viding an  additional  safe-guard. 

Section  "e"  prohibits  the  use  of  two  wires  of  oppo- 
site polarity  in  a  single  tube.  This  is  a  wise  precaution 
in  the  case  of  wires  carrying  large  currents  for  the 
reason  that  a  "  short  circuit"  (or  crossing  of  the  wires) 
might  destroy  the  conduit  or  do  enough  damage  to  pre- 
vent the  withdrawal  and  renewal  of  wires,  before  it 
would  melt  a  large  fuse-wire.  The  note  under  the  defi- 
nition to  Rule  22  allows  two  wires  of  opposite  polarity 
to  be  run  in  one  tube;  but  where  large  wires  are  used  it 
is  no  hardship  to  use  a  tube  for  each  wire,  and  in  gen- 
eral two  tubes  should  be  used  (even  if  they  are  armored) 
except  in  tap  circuits,  *.  <?.,  circuits  running  direct  to 
lamp  or  fixture  outlets  and  carrying  a  small  current. 
In  these  "tap  circuits  "  or  as  they  are  often  termed 
"branch  circuits,"  it  is  often  necessary  to  run  two 
wires  in  one  tube  in  order  to  do  a  neat  and  mechanical 
piece  of  work. 

Section  "f  "  seems  to  call  for  a  needless  refinement; 
but  the  more  nearly  air  and  water-tight  a  conduit  is 
made  the  better.  The  chief  trouble  in  conduits  has 
been  due  to  condensation  of  moisture,  which  would  col- 
lect in  a  pipe  which  sagged  or  was  so  bent  that  a  por- 
tion of  the  pipe  was  lower  than  the  outlets  on  both 
sides  of  it.  The  greatest  care  should  be  exercised  in 
installing  a  conduit,  but  when  it  is  once  properly 
installed  the  results  are  most  satisfactory.  The  cost  of 
a  conduit  system  is  not  as  great  as  is  generally  sup- 
posed, and  we  are  justified  in  demanding  its  use  in  all 
cases  where  it  gives  greater  safety.  In  many  cases  it  is 


LOW    POTENTIAL    SYSTEMS.  105 

cheaper  to  install  iron  armored  conduit  than  to  apply 
any  other  method  that  will  secure  equal  safety  and  reli- 
ability; and  even  where  the  use  of  conduit  materially 
increases  the  first  cost,  of  concealed  work,  it  is  usually 
much  cheaper  in  the  long  run  owing  to  the  saving  in 
maintenance. 


CHAPTER   XII. 

CLASS    C.,    LOW    POTENTIAL    SYSTEMS.       PART  VI. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  23.  DOUBLE 
POLE  SAFETY  CUT-OUTS: — a.  Must  be  in  plain  sight  or  enclosed 
in  an  approved  box,  readily  accessible.  (See  Definitions),  b. 
Must  be  placed  at  every  point  where  a  change  is  made  in  the  size 
of  the  wire  (unless  the  cut-out  in  the  larger  wire  will  protect  the 
smaller),  c.  Must  be  supported  on  bases  of  non-combustible, 
insulating,  moisture-proof  material,  d.  Must  be  supplied  with  a 
plug  (or  other  device  for  enclosing  the  fusible  strip  or  wire)  made 
of  non-combustible  and  moisture-proof  material,  and  so  con- 
structed that  an  arc  cannot  be  maintained  across  its  terminals  by 
the  fusing  of  the  metal,  e.  Must  be  so  placed  that  on  any  com- 
bination fixture  no  group  of  lamps  requiring  a  current  of  six 
amperes  or  more  shall  be  ultimately  dependent  upon  one  cut-out. 
Special  permission  may  be  given  in  writing  by  the  inspector  for 
departure  from  this  rule  in  case  of  large  chandeliers,  f.  All  cut- 
out blocks  must  be  stamped  with  their  maximum  safe-carrying 
capacity  in  amperes. 

DEFINITIONS.  RULE  23.  DOUBLE  POLE  SAFETY  CUT-OUTS: — 
Section  a.  To  be  approved,  boxes  must  be  constructed,  and  cut- 
outs arranged,  whether  in  a  box  or  not,  so  as  to  obviate  any 
danger  of  the  melted  fuse  metal  coming  in  contact  with  any  sub- 
stance which  might  be  ignited  thereby. 

We  have  already  seen  that  a  wire,  or  in  general  any 
conductor,  is  heated  by  the  passage  of  a  current 
through  it.  For  a  given  wire,  the  greater  the  current 
the  greater  the  temperature;  and  for  a  given  current, 
the  thinner  the  wire  the  greater  the  temperature.  The 

(106) 


LOW    POTENTIAL    SYSTEMS.  lO'J 

size  of  wires  must  therefore  be  proportioned  to  the  cur- 
rent they  are  intended  to  carry.  In  practice  low  poten- 
tial circuits  are  always  multiple  arc  circuits,  so  that  the 
current  in  a  circuit,  such  as  we  are  considering,  is  pro- 
portional to  the  number  of  burning  lights  attached  to 
the  circuit,  or  if  motors  are  attached  to  the  circuit,  the 
current  is  also  proportional  to  the  work  which  is  being 
ddne  by  the  motors.  Even  if  the  .wires  are  of  proper 
size  to  carry  a  current  to  supply  all  the  lights  and 
motors  which  are  attached  to  a  circuit,  still  we  are 
liable  to  have  current  leaking  across  from  one  wire 
to  another  of  our  circuit,  if  the  insulation  becomes 
poor;  and  we  may  have  an  immense  current  rushing 
from  one  wire  of  the  circuit  to  another,  in  case  the 
wires  come  into  metallic  contact,  thus  forming  what  we 
call  a  "short  circuit.'"  These  conditions  may  at  any 
time  be  brought  about  by  poor  construction  or  mate- 
rial, imperfect  devices  or  by  some  unforeseen  accident. 
It  is  the  function  of  a  cut-out  to  protect  a  circuit,  if, 
from  a  defect  or  accident,  the  current  becomes  suffi- 
ciently great  to  unduly  heat  the  conductors  of  the  cir- 
cuit or  the  conductors  forming  a  part  of  any  device 
attached  to  the  circuit,  as  for  example  the  wires  upon 
an  electric  motor.  By  unduly  heated  we  do  not  neces- 
sarily mean  heated  to  a  temperature  that  will  ignite 
inflammable  material.  The  wire  must  not  become  heated 
sufficiently  to  injure  the  insulating  qualities  of  its 
covering.  The  cut-out  protects  the  circuit  by  cutting 
it  out,  i.  e.,  by  interrupting  or  as  we  say  opening  the 
circuit,  thus  disconnecting  it  electrically  from  the 
source  of  supply.  As  we  have  already  seen  a  current 


108  THE    NATIONAL    ELECTRICAL    CODE. 

flows  only  in  a  continuous  or  closed  circuit,  and  if  a  gap 
is  made  in  a  circuit  at  any-point,  thus  destroying  its 
continuity,  the  current  instantly  ceases  to  flow  in  that 
circuit.  We  have  also  seen  that  a  current  flows  freely 
in  a  copper  wire  like  water  in  a  pipe,  but  that  it  will 
not  flow  through  an  insulating  substance  such  as  air. 
If  we  insert  an  air  gap  in  a  wire  it  stops  the  flow  of 
electricity  as  effectually  as  we  can  stop  the  flow  of  water 
in  a  pipe  by  stopping  it  up  with  some  solid  material. 
The  device  which  we  use  to  stop  the  flow  of  electricity 
by  making  an  air  gap  in  a  circuit  is  called  a  switch.  A 
switch  interrupts  the  flow  of  an  electrical  current  in 
a  wire  in  a  manner  analogous  to  that  in  which  a  valve 
interrupts  the  flow  of  a  current  of  water  or  steam  in  a 
pipe.  Our  cut-out  corresponds  to  an  automatic  valve 
which  operates  when  the  flow  becomes  excessive. 

To  appreciate  these  comparisons  we  must  bear  in 
mind  that  when  we  interrupt  or  open  an  electrical  cir- 
cuit, what  we  really  do  is  to  replace  a  portion  of  our 
conducting  wire  with  a  barrier  of  insulating  air.  To 
understand  the  uses  and  arrangement  of  cut-outs  we 
must  understand  in  a  general  way  what  a  system  of 
wiring  is  like.  We  have  hitherto  spoken  of  a  circuit  as 
if  it  consisted  simply  of  two  wires,  one  wire  (the  posi- 
tive) carrying  the  current  from  our  dynamo  to  the 
lamps  or  motors,  and  the  other  (the  negative)  conduct- 
ing the  current  back  to  the  dynamo.  In  practice  the 
arrangement  is  not  quite  so  simple.  The  large  wire  or 
cable  leading  from  the  dynamo  is  divided  and  subdi- 
vided, branches  running  off  in  various  directions  to 
motors  or  groups  of  lamps.  This  subdivision  is  carried 


LOW    POTENTIAL    SYSTEMS.  109 

on  until  we  get  to  the  slender  wires  which  are  attached 
directly  to  the  sockets  of  the  lamps.  Every  time  that 
our  positive  wire  branches  off  we  have  a  corresponding 
branching  of  our  negative  wire,  so  that  every  branch 
consists  of  two  wires,  independent  of  one  another  but 
each  connected  back  to  its  respective  pole  of  the  dy- 
namo. The  wiring  of  a  building  therefore  consists  of  a 
double  network  of  wires.  Our  conductors  spread  out 
and  ramify  like  the  branches  of  a  tree.  The  main  con- 
ductors from  the  dynamo  correspond  to  the  trunk.  If 
we  have  circuits  led  off  to  each  floor  of  a  building  these 
correspond  to  the  main  branches.  If  we  subdivide 
these  circuits  and  run  smaller  circuits  to  each  room, 
these  correspond  to  the  smaller  branches,  etc.  The 
smallest  wires  which  connect  to  our  lamp  sockets  cor- 
respond to  the  smallest  twigs,  and  if  we  let  the  incan- 
descent lamps  be  represented  by  the  leaves  of  the  tree 
our  figure  is  complete,  except  that  to  represent  our 
wiring  completely  we  must  imagine  that  (without  break- 
ing off  any  branches  or  twigs),  we  split  our  tree  in 
halves,  splitting  trunk,  branches,  twigs  and  all,  clear  to 
the  point  where  the  leaves  are  attached.  This  analogy 
of  a  tree  has  always  been  present  in  the  mind  of  the 
wireman,  even  if  he  did  not  stop  to  consider  it.  We 
speak  of  "trunk"  lines,  "branch"  circuits,  etc.,  and  the 
names  themselves  suggest  the  arrangement  without 
explanation.  In  the  early  days,  wiring  was  laid  out  in 
a  building  without  any  special  order  or  system.  From 
the  main  wires  branches  were  led  off  and  from  these 
branches  were  run  smaller  branches  and  so  on,  the 
wires  decreasing  in  size  with  each  division.  This  style 


110  THE    NATIONAL    ELECTRICAL    CODE. 

of  wiring  was  called  the  "  Tree  System."  The  arrange- 
ment was  as  fortuitous  as  that  of  the  branches  of  a  tree 
and  too  frequently  the  quality  of  the  lights  was  as 
varied  as  that  of  the  fruit  on  a  tree.  To-day  the  wiring 
of  a  building  is  done  on  more  scientific  principles.  The 
conductors  divide  branch  and  subdivide,  but  they  are 
arranged  in  a  more  orderly  and  systematic  manner. 
The  changes  of  arrangement  are  interesting  but  it  is  not 
necessary  to  devote  space  here  to  a  detailed  description 
of  them.  The  typical  wiring  system  of  to-day  is  laid  out 
in  much  the  same  manner  as  a  well  designed  system  of 
gas  piping,  each  pipe  corresponding  to  a  pair  of  wires. 

We  have  used  the  word  "circuit,"  sometimes  to 
describe  a  pair  of  conductors  with  all  their  branches, 
and  again  to  describe  one  of  the  branches;  but  we 
believe  the  connection  in  which  the  word  is  used  will 
show  which  way  it  is  applied  in  any  particular  case. 

When  we  send  a  current  of  electricity  however  small 
through  a  wire,  the  wire  becomes  heated.  If  we 
increase  the  current  sufficiently  we  can  heat  the  wire 
red  hot.  A  further  increase  wivll  heat  it  white  hot  (an 
example  of  this  is  the  loop  in  an  incandescent  lamp). 
We  can  carry  this  still  further  and  by  making  our  cur- 
rent large  enough  we  can  melt  or  fuse  our  wire.  A 
fusible  cut-out  is  simply  a  short  piece  of  wire  (usually 
of  a  material  which  fuses  at  a  low  temperature)  inserted 
into  one  of  the  conductors  of  a  circuit,  and  of  such 
size  that  it  will  be  fused  by  the  passage  of  a  current 
somewhat  less  than  sufficient  to  unduly  heat  the  con- 
ductor itself.  In  practice  the  piece  of  fusible  wire  is 
called  a  "fuse."  The  device  for  containing  the  fuse 


LOW    POTENTIAL    SYSTEMS.  Ill 

and  connecting  it  to  the  conductor  is  called  a  "  cut-out 
block"  or  "fuse  block."  The  name  ctit-out  is  used  to 
include  both  the  fuse  block  and  fuse.  Where  a  fuse 
is  inserted  into  both  the  positive  and  negative  sides  of 
a  circuit,  both  fuses  being  placed  upon  one  fuse  block, 
the  device  is  called  a  "  double  pole  cut-out."  In  early 
days  circuits  were  protected  only  by  single  pole  cut- 
outs, i.  e.,  by  haying  a  fuse  inserted  into  one  conductor 
of  a  circuit  only.  This  practice  has  been  abandoned, 
and  the  code  allows  only  double  pole  cut-outs  in  all  cases. 
The  reason  of  this  is  that  single  pole  cut-outs,  while 
effective  to  prevent  an  individual  circuit  from  an  excess 
of  current,  will  not  necessarily  prevent  an  excess  of 
current  flowing  into  a  wire  when,  by  any  defect  or  acci- 
dent, an  electrical  connection  is  made  between  the /#.$•- 
itive  conductor  of  one  circuit  and  the  negative  conductor 
of  another  circuit.  Another  point  which  should  not  be 
overlooked  in  this  connection  is  that  by  using  double 
pole  cut-outs,  we  can  at  any  time  disconnect  any  cir- 
cuit from  the  rest  of  the  system  by  simply  removing 
the  fuses,  thus  enabling  us  to  quickly  and  easily  test 
the  circuit.  Section  "a"  of  Rule  23  should  be  observed 
in  order  that  cut-outs  may  be  easily  inspected.  While  a 
cut-out  is  a  source  of  safety  if  properly  designed  and 
installed,  it  may  become  a  danger  point  in  case  it  is 
not  constructed,  installed  and  maintained  in  the  man- 
ner required  by  the  code.  Convenience  also  dictates 
that  cut-outs  shall  be  so  placed  that  they  can  be  easily 
found  and  easily  reached  when  it  becomes  necessary  to 
make  a  test  or  to  replace,  a  fuse  which  has  melted. 
The  parenthetical  clause  in  section  "  b  "  shows  us  how 


112  THE    NATIONAL    ELECTRICAL    CODE. 

to  determine  the  size  and  location  of  cut-outs.  Origi- 
nally, the  regulations  of  the  underwriters  required  that 
cut-outs  must  be  placed  at  every  point  where  a  change  is 
made  in  the  size  of  the  wire.  When  this  rule  was  made 
it  was  customary  to  do  the  wiring  of  the  "  tree  system  " 
almost  exclusively.  In  this  system  the  wires  were 
reduced  in  size  every  time  that  they  branched,  the  size 
of  the  wire  in  any  branch  being  proportional  to  the 
number  of  lamps  for  which  it  carried  current.  The 
rule  was  a  good  one  at  the  time  it  was  made,  as  it  prac- 
tically required  a  cut  out  to  be  placed  at  every  point 
where  the  wires  branched,  and  such  an  arrangement 
was  the  only  one  that  made  it  possible  to  cut  up  such  a 
system  of  conductors  so  that  one  could  test  it  out  and 
locate  faults.  The  method  of  wiring  on  the  tree  system 
with  cut-outs  wherever  the  size  of  wire  changed  gave 
safety,  but  it  required  a  needless  number  of  cut-outs, 
and  the  points  where  the  wires  branched  were  not  always 
convenient  or  proper  points  at  which  to  locate  cut-outs. 
To-day  we  secure  safety  with  a  smaller  number  of  cut- 
outs. The  wiring  is  arranged  so  that  the  cut-outs  are 
not  distributed  all  over  a  building,  but  are  bunched  in 
convenient  distributing  centers,  where  they  can  be  pro- 
tected, and  at  the  same  time  are  easily  accessible. 

It  is  usually  convenient  to  run  but  one  circuit  to  a 
fixture,  especially  when  the  lights  are  to  be  controlled 
by  a  switch.  The  code,  therefore,  allows  some  discre- 
tion to  the  inspector  in  this  kind  of  work.  It  is  a  pretty 
safe  rule  to  allow  not  over  about  ten  incandescent 
lamps,  /.  <?.,  five  or  six  amperes  on  any  lamp  circuit. 
Exceptions  may  be  made  to  this  rule,  but  only  when  we 


LOW    POTENTIAL    SYSTEMS.  113 

are  certain  that  the  wires  and  devices  are  all  suitable 
for  carrying  a  greater  current.  We  do  not  need  to  set 
such  a  low  limit  in  order  to  protect  our  circuits,  for  we 
can  always  accomplish  that  by  proportioning  out  the 
fuses  to  the  size  of  the  wires,  but  on  a  circuit  carrying 
incandescent  lamps  it  is  best  not  to  allow  a  current  of 
more  than  about  five  or  six  amperes,  as  an  arc  formed 
by  a  greater  current  than  this  will  demolish  any  ordi- 
nary socket. 

Section  "f  "  is  a  good  rule,  but  it  might  be  improved 
by  stating  that  the  capacity  be  marked  on  the  face  of 
the  cut-out  block  so  that  an  inspector  can  tell  at  a 
glance  if  it  is  all  right.  A  current  heats  any  conductor 
through  which  it  flows,  and  a  fuse  block  carries  con- 
ductors in  the  form  of  metal  connections  to  which  the 
wires  and  fuses  are  attached.  It  is  just  as  important  to 
have  these  connections  large  enough  as  it  is  to  have  the 
wires  of  a  proper  size.  The  "  maxi'mum  safe  carrying 
capacity  in  amperes  "  of  any  conductor  is  the  greatest 
current  in  amperes  which  it  will  carry  continuously 
without  becoming  unduly  heated.  "  Unduly  heated  " 
is  a  loose  expression,  and  it  does  not  mean  any  definite 
temperature,  as  the  temperature  which  is  allowable  in 
any  particular  case  depends  upon  a  number  of  circum- 
stances. Generally  speaking,  a  bare  metal  conductor 
is  considered  unduly  heated  if  it  is  so  hot  that  one 
cannot  with  comfort  hold  it  grasped  firmly  in  the  bare 
hand.  With  the  ordinary  hand,  this  means  a  tempera- 
ture of  about  150  to  175  degrees  Fahrenheit.  We  will 
consider  the  question  of  carrying  capacity  more  fully 
in  our  next  chapter. 


CHAPTER    XIII. 

CLASS    C,    LOW    POTENTIAL    SYSTEMS.        PART    VII. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  24.  SAFETY 
FUSES: — a.  Must  all  be  stamped  or  otherwise  marked  with  the 
number  of  amperes  they  will  carry  indefinitely  without  melting. 
b.  Must  have  fusible  wires  or  strips  (where  the  plug  or  equivalent 
device  is  not  used),  with  contact  surfaces  or  tips  of  harder  metal, 
soldered  or  otherwise,  having  perfect  electrical  connections  with 
the  fusible  part  of  the  strip,  c.  Must  all  be  so  proportioned  to 
the  conductors  they  are  intended  to  protect  that  they  will  melt 
before  the  maximum  safe-carrying  capacity  of  the.  wire  is 
exceeded. 

25.  TABLE  OF  CAPACITY  OF  WIRES: — It  must  be  clearly  under- 
stood that  the  size  of  the  fuse  depends  upon  the  size  of  the  smallest 
conductor  it  protects,  and  not  upon  the  amount  of  current  to  be 
used  on  the  circuit.  Below  is  a  table  showing  the  safe-carrying 
capacity  of  conductors  of  different  sizes  in  Brown  &  Sharpe 
gauge,  which  must  be  followed  in  the  placing  of  interior  con- 
ductors : — 

TABLE   A — CONCEALED    WORK.  TABLE    B— OPEN    WORK. 

B.  &  S.  G.          Amperes.  Amperes. 

oooo 218  312 

ooo 181  262 

oo 150  220 

o 125  185 

I  105  156 

2 88 131 

3 75  no 

4 63  92 


LOW    POTENTIAL  .SYSTEMS.  115 

TABLE   A — CONCEALED   WORK.  TABLE    B— OPEN    WORK. 

B.  6°  S.  G.  Amperes.  Amperes. 

5 53   77 

6 45   65 

8 33   46 

10 25 32 

12     17    23 

14 12 16 

16 6    8 

18 3 5 

NOTE. — By  "open  work"  is  meant  construction  which  admits 
of  all  parts  of  the  surface  of  the  insulating  covering  of  the  wire 
being  surrounded  by  free  air.  The  carrying  capacity  of  16  and 
18  wire  is  given,  but  no  wire  smaller  than  14  is  to  be  used  except 
as  allowed  under  Rules  18  (a)  and  27  (d). 

Before  taking  up  the  subject  of  fuses,  let  us  consider 
more  fully  the  requirements  of  Rule  23  (the  text  of 
which  was  printed  in  our  last  chapter)  relating  to  cut- 
outs. Section  "b"  may  be  stated  as  follows:  "  Every 
wire  shall  be  protected  by  a  fuse  of  such  a  size  that  it 
will  melt  before  the  wire  becomes  unduly  heated."  Cut- 
out bases  or  "blocks"  are  made  of  marble,  slate,  glass 
or  porcelain.  For  ordinary  sizes  porcelain  is  now  uni- 
versally used.  It  is  the  best  material,  as  it  is  strong, 
is  easily  moulded  into  convenient  forms,  is  cheap,  and, 
when  thoroughly  vitrified,  is  a  first-class  insulator. 
When  a  fuse  melts  and  a  circuit  carrying  a  current  is 
opened,  we  of  course  have  a  flash,  and  the  greater  the 
current  the  greater  the  flash.  Section  "  d  "  requires 
such  a  design  of  cut-out  as  shall  prevent  the  blowing  of 
a  fuse  from  igniting  any  adjacent  inflammable  material. 
Safety  is  usually  secured,  first,  by  enclosing  the  cut- 
outs in  a  box  or  cabinet  with  a  fire-proof  lining;  sec- 


Il6  THE    NATIONAL    ELECTRICAL    CODE. 

ond,  by  having  the  cut-out  so  designed  that  each  fuse 
is  covered.  This  last  is  accomplished  by  providing  the 
fuse  block  with  a  mica  or  porcelain  cover,  or  by  using 
a  plug,  as  mentioned  in  section  "d."  The  "plug"  is 
a  device  which  connects  the  fuse  with  the  circuit  in  the 
same  manner  that  an  Edison  lamp  is  attached  to  a  cir- 
cuit. The  fuse  plug  is  just  like  the  base  of  an  Edison 
incandescent  lamp,  except  that  a  piece  of  fuse  \vire 
replaces  the  wires  leading  to  the  loop  or  filament,  and 
that  the  base  has  a  metal  cover  to  prevent  the  melted 
metal  from  blowing  out.  These  plug  cut-outs  are  used 
for  circuits  carrying  currents  up  to  about  15  amperes; 
and  for  small  currents  they  are  both  convenient  and 
safe. 

A  "combination  fixture,"  mentioned  in  section  "c," 
is  a  chandelier  or  bracket,  designed  to  carry  both  gas 
and  electric  lights.  A  circuit  to  a  fixture  ought  to  be 
protected  by  a  small  fuse  if  possible.  From  the  nature 
of  its  construction,  most  combination  fixtures  have  to 
carry  small  wires.  Again,  it  would  be  disastrous  to 
have  an  arc  of  many  amperes  formed  in  a  combination 
fixture,  as  it  might  burn  a  hole  in  a  gas  pipe  and  ignite 
the  gas. 

We  have  seen  that  the  branch  blocks  must  be  so  pro- 
portioned that  the  conducting  metal  will  carry  the  cur- 
rent without  overheating,  and  that  in  order  that  we  may 
be  sure  of  having  connections  of  proper  size,  the  blocks 
must  be  marked  with  the  maximum  number  of  amperes 
that  the  cut-out  is  designed  to  carry.  We  now  come 
to  the  subject  of  "fuses. "  A  fuse  has  been  described  as 
a  piece  of  wire  of  such  a  size  and  material  that  it  will 


LOW    POTENTIAL    SYSTEMS.  llj 

melt  before  the  current  becomes  sufficiently  great  to 
unduly  overheat  the  conductors  of  our  circuit.  The 
fuse  is  usually  of  a  material  which  is  a  poor  conductor, 
and  which  will  melt  at  a  low  temperature.  It  is  not 
essential,  however,  that  such  a  material  be  used.  Any 
metal  may  be  used  if  the  wire  is  made  of  the  proper 
size,  but  by  using  a  poor  conductor  and  a  metal  which 
fuses  at  a  low  temperature,  a  wire  can  be  made  which, 
though  of  a  respectable  size,  will  be  fused  by  a  small 
current.  The  question  of  the  best  material  for  fuses  is 
still  a  mooted  one,  but  experience  has  thus  far  led  to 
the  use  of  some  such  metal  as  above  described.  The 
most  common  material  used  is  an  alloy  of  lead,  such  as 
lead,  antimony  and  tin. 

We  have  already  seen  that  the  fuse  must  be  of  such  a 
size  as  to  melt  before  the  current  can  overheat  the 
smallest  wire  depending  upon  it  for  protection.  As 
fuses  differ  in  material,  the  appearance  of  a  fuse  is  no 
indication  of  the  number  of  amperes  which  it  will  carry 
without  melting.  All  fuses  ought,  therefore,  to  be 
marked  so  that  anyone  can  tell  how  many  amperes  it 
will  take  to  melt  it.  Unless  this  rule  is  observed,  cir- 
cuits will  seldom  be  properly  fused,  and,  what  is  more, 
no  inspector  can  tell  whether  or  not  they  are  properly 
fused. 

Section  "b,"  though  often  violated,  is  one  which 
should  always  be  observed.  This  rule  prohibits  the 
fastening  of  fuse  wires  into  a  cut-out  block  by  fastening 
the  ends  of  a  soft  wire  under  the  head  of  a  screw.  The 
reason  for  this  is  that  a  soft  metal  like  lead  cannot  be 
held  firmly  in  place  by  clamping  it.  The  metal  will 


Il8  THE    NATIONAL    ELECTRICAL    CODE. 

gradually  but  surely  spread  out  under  pressure  until  the 
wire  becomes  loose  in  its  fastenings.  Wherever  we 
have  a  joint  or  contact  there  is  resistance.  The  poorer 
the  contact  the  greater  the  resistance,  and  consequently 
the  more  the  joint  will  be  heated  by  a  given  current. 
When,  therefore,  our  joint  becomes  loose  it  begins  to 
heat.  Again,  as  soon  as  the  joint  becomes  loose,  the 
surface  of  the  fuse  is  exposed  to  the  air  and  it  quickly 
oxidizes.  This  oxidation  still  further  increases  the 
resistance  of  the  joint,  and  soon  we  find  that  the  fuse 
will  blow  with  a  current  much  smaller  than  that  for 
which  it  was  designed.  The  blowing  of  the  fuse  in 
itself  would  do  no  special  harm,  but  the  chances  are 
that  it  will  be  replaced  by  a  larger  fuse,  so  that  wire 
will  not  be  properly  protected.  Aside  from  the  ques- 
tion of  safety,  it  is  poor  engineering  to  install  a  safety 
device  that  will  not,  as  nearly  as  possible,  furnish  the 
same  protection  at  all  times.  Again,  in  the  case  of  small 
fuse  wires  it  is  necessary  to  have  some  sort  of  tip  to  the 
wire  in  order  to  have  a  place  on  which  to  mark  the 
capacity  of  the  fuse.  Section  "c"  is  a  rule  which  we 
have  already  considered  under  the  subject  of  cut-outs. 
We  have  spoken  of  a  fuse  as  a  wire  in  the  same  way 
that  we  have  spoken  of  our  conductors  as  wires.  As  a 
matter  of  fact,  our  conductor,  if  very  large,  may  con- 
sist of  a  bar  of  copper  instead  of  a  wire,  and  in  the 
same  way  our  fuse,  if  large,  may  be  (and  usually  is)  a 
flat  strip  of  "fuse  metal."  Such  fuses  are  called  fuse 
strips.  Whatever  the  form  of  our  conductor  or  our 
fuse,  the  fuse  must  be  proportioned  to  the  size  of  the 
smallest  conductor  which  it  has  to  protect.  A  conductor 


LOW   POTENTIAL    SYSTEMS.  1 19 

is  properly  protected  when  there  is  between  it  and  the 
dynamo  a  fuse  which  will  be  melted  by  a  current  which 
is  smaller  than  the  "  maximum  safe  carrying  capacity" 
of  the  conductor. 

This  brings  us  to  the  subject  of  carrying  capacity  of 
wires.  The  term  "safe  carrying  capacity,"  or,  as  we 
more  commonly  say,  "carrying  capacity,"  of  a  wire  is 
a  term  quite  commonly  misunderstood.  It  has,  how- 
ever a  very  definite  meaning.  The  safe  carrying  capa- 
city of  a  wire  is  the  maximum  current  in  amperes  which 
it  is  allowed  to  carry  by  the  underwriters.  The  safe 
carrying  capacity  for  any  ordinary  size  of  wire  is  given 
in  the  code,  in  the  table  which  is  printed  above.  This 
table  gives  the  maximum  currents  that  the  various  sizes 
of  wires  will  carry  without  unduly  overheating.  The 
values  have  been  determined  by  calculation  and  expe- 
rience. We  have  stated  that  a  wire  is  unduly  over- 
heated when  it  becomes  hot  enough  to  injure  the 
insulating  material  with  which  it  is  covered.  Of  course, 
one  kind  of  insulation  will  stand  a  higher  temperature 
without  injury  than  another,  and  again,  the  tempera- 
ture to  which  a  given  current  will  heat  a  certain  sized 
wire  will  depend  upon  the  original  temperature  of  the 
wire  and  the  opportunity  which  it  has  for  cooling.  We 
cannot,  however,  have  a  different  table  of  carrying 
capacities  for  every  kind  of  wire  and  construction,  and 
the  table  given  above  is  one  which  leaves  a  margin  of 
safety  in  any  ordinary  construction.  Upon  examining 
the  above  table,  the  reader  will  find  that  apparently 
there  is  no  direct  relation  between  the  size  of  a  wire 
and  the  current  which  it  is  allowed  to  carry.  It  may 


I2O  THE    NATIONAL    ELECTRICAL    CODE. 

be  well,  therefore,  to  take  a  little  space  to  show  why 
this  is  so;  as  such  an  explanation  will  show  the  impor- 
tance and  necessity  of  a  table  of  maximum  safe-carry- 
ing capacities. 

We  have  seen  that  any  conductor  offers  a  resistance 
to  the  flow  of  a  current  of  electricity  in  a  manner  anal- 
ogous to  that  in  which  friction  opposes  the  flow  of  water 
in  a  pipe.  We  have  also  seen  that  it  is  necessary  to 
expend  work  to  overcome  resistance,  and  that  this  work 
represents  a  loss  of  energy,  the  same  as  when  work  is 
done  to  overcome  friction.  This  lost  energy,  like  the 
energy  lost  in  overcoming  friction,  is  transferred  into 
heat,  so  that  the  electrical  energy  lost  in  a  wire  has  the 
effect  of  raising  the  temperature  of  the  wire.  The  cal- 
culation of  the  loss  of  energy  in  a  wire  carrying  an 
electrical  current  is  a  much  simpler  matter  than  the 
calculation  of  the  loss  from  friction  in  a  water  pipe. 
The  loss  per  foot  in  a  given  wire  is  proportional  to  the 
square  of  the  current,  i.  e.,  the  loss  in  power  or  the  heat 
generated  will  be  four  times  as  great  with  a  current  of 
two  amperes  as  with  a  current  of  one  ampere.  Again, 
with  a  given  current  the  loss  is  inversely  proportional  to 
the  sectional  area  or  "cross  section  "  of  the  wire;  so 
that,  if  we  have  two  wires,  one  one-half  of  an  inch  in 
diameter  and  another  one-fourth  of  an  inch  in  diame- 
ter, the  sectional  area  of  the  first  wire  will  be  four  times 
as  great  as  that  of  the  second,  and  if  the  two  wires 
carry  the  same  current,  the  loss  in  the  larger  wire  will 
be  only  one-fourth  of  that  in  the  thinner  one.  It  would 
seem  ^\.  first  thought,  therefore,  that  the  larger  wire 
could  be  allowed  to  carry  four  times  the  current  of  the 


LOW    POTENTIAL    SYSTEMS.  121 

smaller  one  without  becoming  any  hotter.  The  prob- 
lem is  not,  however,  quite  as  simple  as  that.  Let  us 
take  the  example  of  the  two  wires,  the  first  one-half 
inch  and  the  second  one-fourth  inch  in  diameter. 

Suppose  that  each  wire  carries  a  current  of  one 
ampere;  then  the  loss  in  the  larger  wire  will  be  but 
one-fourth  that  in  the  smaller  wire,  as  the  larger  wire 
has  four  times  the  area,  and  therefore  one-fourth  the 
resistance  of  the  smaller.  If  now  we  increase  the  cur- 
rent in  the  large  wire  to  four  amperes  we  shall  increase 
the  loss,  or,  what  is  the  same  thing,  we  shall  increase 
the  amount  of  heat  generated  not  four  but  sixteen  times, 
or  in  the  ratio  of  the  square  of  the  currents.  The  result 
will  be,  therefore,  that  the  heat  generated  will  be  four 
times  that  generated  by  one  ampere  in  the  small  wire. 
As  the  larger  wire  has  four  times  the  mass  of  metal  in 
the  smaller  one,  it  might  still  seem  as  if  the  temperature 
of  the  two  wires  would  be  the  same;  but  the  tempera- 
ture of  the  wire  is  determined,  not  only  by  the  amount 
of  heat  generated,  but  by  the  amount  of  heat  which  the 
wire  loses  in  a  given  time.  When  the  amount  of  heat 
generated  in  a  given  time  is  equal  to  that  lost  in  the 
same  time,  the  wire  comes  to  a  fixed  temperature,  and 
the  faster  the  heat  can  be  conducted  or  radiated  from 
the  surface  of  the  wire  the  lower  will  be  that  tempera- 
ture. (This  is  the  reason  that  we  have  two  tables  of 
carrying  capacity,  one  for  wire  suspended  freely  in  the 
air  and  another  where  the  wires  are  enclosed  so  that  the 
heat  does  not  get  a  chance  to  radiate  into  the  cooler 
air.)  The  amount  of  heat  generated 'in  our  larger  wire 
is  four  times  that  generated  in  the  smaller  one,  but  the 


122  THE    NATIONAL    ELECTRICAL   CODE. 

amount  of  heat  lost  by  radiation  is  proportional  to  the 
surface  exposed,  and  the  larger  wire  has  not  four,  but 
only  two  times  the  exposed  surface  of  the  wire  of  one- 
half  the  diameter.  The  result  is  that  the  large  wire 
will  get  hotter  with  four  amperes  than  the  small  wire 
will  with  one  ampere.  It  follows,  therefore,  that  if  one 
wire  has  twice  the  sectional  area  of  another,  it  will 
have  something  less  than  twice  the  safe-carrying  capa- 
city. 

Upon  consulting  the  table,  we  will  see  that  while  a 
No.  o  wire  has  almost  exactly  twice  the  area  of  a  No.  3 
wire,  the  No.  3  wire  is  allowed  to  carry  75  amperes, 
while  the  No.  o  wire  is  allowed  to  carry  only  125  am- 
peres. The  greater  the  difference  in  the  sizes,  the  more 
conspicuously  is  this  shown  in  the  table.  While  a  No. 
10  wire  may  carry  25  amperes,  a  No.  o  wire  (with  ten 
times  the  sectional  area)  is  allowed  to  carry  only  five 
times  that  current.  The  calculation  of  the  relative 
currents  allowed  for  different  sizes  of  wires  involves 
considerable  figuring,  and  a  table  of  "capacities"  is  a 
most  useful  thing,  and  no  wire  used  in  electrical  con- 
struction should  ever  be  allowed  to  carry  a  greater  cur- 
rent than  that  allowed  in  the  table.  The  table  of 
capacities  shows  what  current  a  wire  may  carry  with 
safety,  but  the  wireman  must  not  make  the  mistake  of 
thinking  that  the  table  is  any  guide  to  the  size  of  wire 
to  be  selected  for  any  particular  circuit.  The  wire  must 
not  be  smaller  than  that  given  in  the  table,  but  in  many 
cases  the  wire  must  be  larger  in  order  to  give  the  proper 
pressure  at  the  lamps.  The  temperature  of  a  wire  is 
determined  by  its  size,  the  current  which  it  carries  and 


LOW    POTENTIAL    SYSTEMS.  123 

by  its  surroundings,  it  is  independent  of  the  length.  The 
total  amount  of  energy  lost  in  a  wire  is  proportional  to 
its  length,  so  that  in  calculating  a  wire  from  an  engi- 
neering standpoint,  the  length  of  the  circuit  must  be 
considered.  The  proper  way  to  select  the  size  of  wire 
required  for  any  particular  case  is  to  calculate  the  size 
which  will  give  the  maximum  loss  consistent  with  good 
service,  and  then  consult  the  table  of  "capacities."  If 
the  calculated  size  is  larger  than  that  allowed  by  the 
code  for  the  current  to  be  carried,  use  it;  if  it  is  smaller 
than  the  size  allowed  by  the  code,  then  take  the  size 
allowed  in  the  table. 

The  table  of  safe-carrying  capacities  does  not  apply 
to  wires  used  in  the  construction  of  dynamos  or  motors 
nor  to  the  wires  used  in  rheostats.  The  rules  which  we 
have  already  considered  demand  that  the  installation  of 
machines,  rheostats,  etc.,  shall  be  so  made  that  they 
may  become  hot  without  causing  a  hazard. 


CHAPTER    XIV. 

CLASS    C.,     LOW    POTENTIAL    SYSTEMS.       PART    VIII. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  26.  SWITCHES: — 
a.  Must  be  mounted  on  moisture-proof  and  non-combustible 
bases  such  as  slate  or  porcelain,  b.  Must  be  double  pole  when 
the  circuits  which  they  control  supply  more  than  six  i6-candle- 
power  lamps  or  their  equivalent,  c.  Must  have  a  firm  and  secure 
contact;  must  make  and  break  rapidly,  and  not  stop  when  motion 
has  once  been  imparted  by  the  handle,  d.  Must  have  carrying 
capacity  sufficient  to  prevent  heating,  c.  Must  be  placed  in  dry, 
accessible  places  and  be  grouped  as  far  as  possible,  being  mounted, 
when  practicable,  upon  slate  or  equally  non-combustible  back 
boards.  Jackknife  switches,  whether  provided  with  friction  or 
spring  stops,  must  be  so  placed  that  gravity  will  tend  to  open 
rather  than  close  the  switch. 

FIXTURE  WORK: — a.  In  all  cases  where  conductors  are  con- 
cealed within  or  attached  to  gas  fixtures,  the  latter  must  be  insu- 
lated from  the  gas  pipe  system  of  the  building  by  means  of 
approved  joints.  The  insulating  material  used  in  such  joints 
must  be  of  a  substance  not  affected  by  gas,  and  that  will  not 
shrink  or  crack  by  variation  jn  temperature.  Insulating  joints, 
with  soft  rubber  in  their  construction,  will  not  be  approved.  (See 
Definition.)  b.  Supply  conductors  and  especially  the  splices  to 
fixture  wires,  must  be  kept  clear  of  the  grounded  part  of  gas  pipes, 
and  where  shells  are  used  the  latter  must  be  constructed  in  a 
manner  affording  sufficient  area  to  allow  this  requirement  c. 
When  fixtures  are  wired  outside,  the  conductors  must  be  so 
secured  as  not  to  be  cut  or  abraded  by  the  pressure  of  the  fasten- 
ings or  motion  of  the  fixture,  d.  All  conductors  for  fixture  work 
must  have  a  water-proof  insulation  that  is  durable  and  not  easily 

(124) 


LOW    POTENTIAL    SYSTEMS.  125 

abraded,  and  must  not  in  any  case  be  smaller  than  No.  18  B.  & 
S.,  No.  20  B.  W.  G.,  No.  2  E.  S.  G.  e.  All  burrs  or  fins  must  be 
removed  before  the  conductors  are  drawn  into  a  fixture,  f.  The 
tendency  to  condensation  within  the  pipes  should  be  guarded 
against  by  sealing  the  upper  end  of  the  fixture,  g.  No  combina- 
tion fixture  in  which  the  conductors  are  concealed  in  a  space  less 
than  one  fourth  inch  between  the  inside  pipe  and  the  outside 
casing  will  be  approved,  h.  Each  fixture  must  be  treated  for 
"contacts"  between  conductors  and  fixtures,  for  "short  circuits" 
and  for  ground  connections  before  the  fixture  is  connected  to  its 
supply  conductors,  i.  Ceiling  blocks  of  fixtures  should  be  made 
of  insulating  material;  if  not,  the  wires  in  passing  through  the 
plate  must  be  surrounded  with  hard  rubber  tubing. 

28.  ARC  LIGHTS  ON  Low  POTENTIAL  CIRCUITS: — a.  Must  be 
supplied  by  branch  conductors  not  smaller  than  No.  12  B.  &  S. 
gauge,  b.  Must  be  connected  with  main  conductors  only  through 
double  pole  cut-outs. 

DEFINITION.  RULE  27.  FIXTURE  WORK: — Section  a.  Insu- 
lating joints  to  be  approved  must  be  entirely  made  of  material 
that  will  resist  the  action  of  illuminating  gases,  and  will  not  give 
way  or  soften  under  the  heat  of  an  ordinary  gas  flame.  They 
shall  be  so  arranged  that  a  deposit  of  moisture  will  not  destroy 
the  insulating  effect,  and  shall  have  an  insulating  resistance  of 
250,000  ohms  between  the  gas  pipe  attachments,  and  be  suffi- 
ciently strong  to  resist  the  strain  they  will  be  liable  to  in  attach- 
ment. 

In  this  chapter  and  the  one*  which  follows  it,  we  will 
cover  what  remains  of  the  code,  upon  the  subject  of 
low  potential  systems.  This  portion  of  the  code  deals 
with  the  details  of  electrical  construction  and  electrical 
appliances.  While  the  principles  governing  construction 
and  design  have  been  covered  in  the  preceding  chapters 
of  the  code,  still  there  are  certain  mistakes  which  have 
been  so  repeatedly  and  persistently  made  year  after 
year,  that  rules  upon  these  particular  points  are  neces- 


126  THE    NATIONAL    ELECTRICAL    CODE. 

sary.  In  electrical,  as  in  mechanical  construction, 
"The  strength  of  any  structure  is  the  strength  of  its 
weakest  part."  The  points  referred  to  in  this  part  of 
the  code  are  those  which  experience  has  shown  to  be 
weak  points  in  our  electrical  structure.  It  will  be  noted 
that  the  rules  at  the  head  of  this  chapter,  and  those 
immediately  following,  state  specifically  that  certain 
things  shall  and  certain  things  shall  not  be  done.  It  is 
impossible  in  our  allotted  space  to  describe  the  details 
of  electrical  construction  or  electrical  appliances.  To 
do  this  so  as  to  give  an  intelligent  idea  of  an  electrical 
device,  to  one  who  has  not  seen  the  device,  would 
require  the  use  of  illustrations  or  diagrams  and  would 
consume  much  space.  We  would  suggest  that  those  of 
our  readers  who  are  not  familiar  with  the  appearance 
of  the  appliances  referred  to  in  the  code,  take  this 
occasion  to  inspect  the  things  themselves,  either  at  an 
electrical  supply  store  or  in  some  electric  plant,  as 
a  knowledge  of  what  the  most  common  electrical 
devices  look  like  cannot  fail  to  be  interesting  and  will 
aid  one  more  than  anything  else  to  understand  their 
uses  and  requirements.  We  make  this  suggestion,  as 
the  names  of  things  electrical  are  often  misleading;  for 
example:  a  switch  might  be  expected  to  be  a  device  for 
switching  a  current  from  one  path  to  another,  while,  as 
a  matter  of  fact,  a  switch  is  the  name  used  in  the  code 
for  a  device  to  interrupt  or  open  a  circuit. 

Switches. — We  have  seen  that  a  branch  circuit,  to  a 
lamp  or  to  a  group  of  lamps  or  to  a  motor,  consists  of 
two  wires,  one  a  positive  wire,  by  which  the  current  is 
led  from  the  positive  wire  of  the  main  circuit  to  the 


OF  THE 

UNIVERSITY 

LOW    POTENTIAL    SfrSTEMSc  - 


lamp  or  motor,  and  the  other  or  negative  wire,  by 
which  the  current  returns  to  the  negative  wire  of  our 
main  circuit.  When  a  switch  is  so  constructed  as  to 
open  both  of  these  wires  at  the  same  time,  it  is  called  a 
"double  pole  switch."  Such  switches  are  required  by 
the  code  for  all  circuits  carrying  more  than  six  lights, 
that  is  to  say  for  any  circuit  carrying  a  current  of  over 
three  amperes.  This  is  desirable  for  two  reasons:  First, 
it  is  necessary  to  have  a  double  pole  switch  in  order  to 
completely  disconnect  a  circuit  from  the  rest  of  the 
system,  so  as  to  test  it.  Second,  when  we  use  a  double 
pole  switch,  we  make  a  break  in  two  places  at  the  same 
time,  so  that  the  arc,  which  is  momentarily  formed  on 
the  opening  of  a  circuit  carrying  current,  is  divided  and 
the  danger  of  burning  the  switch  is  thereby  greatly 
decreased.  A  "firm  contact"  is  necessary  as  every  con- 
tact offers  a  resistance  to  the  flow  of  current,  and  the 
poorer  the  contact  the  greater  the  resistance.  Good 
contact  is  maintained  by  good  mechanical  construction 
and  by  having  a  sufficiently  large  surface  of  contact. 
As  an  arc  is  formed  on  breaking  a  current,  the  quicker 
the  break  the  better  for  the  switch.  In  order  that  the 
break  must  be  quick,  the  switch  must  be  so  designed 
that  the  moving  part  is  thrown  by  a  spring  which,  as 
soon  as  it  acts  on  the  switch,  throws  it  wide  open.  It 
is  also  desirable  to  have  a  switch  clgse  quickly,  and  this 
too  is  accomplished  by  the  use  of  a  spring.  When  a 
switch  is  opened  and  closed  by  a  spring,  it  is  called  a 
"snap"  switch.  This  style  of  switch  is  what  is  referred 
to  in  section  "c"  Rule  26.  Snap  switches  "are  required 
for  all  circuits,  except  circuits  carrying  large  currents. 


128  THE    NATIONAL    ELECTRICAL    CODE. 

For  large  currents  the  switches  are  of  the  "jackknife 
type  and  are  placed  on  a  switchboard  or  in  a  cut-out 
cabinet.  Section  "  d  "  refers  to  the  thickness  of  con- 
ducting metal.  A  switch  should  not  heat  enough  so 
that  the  heat  can  be  noticed  upon  feeling  of  it  with  the 
bare  hand.  The  material  of  which  most  switches  are 
made  is  not  more  than  half  as  good  a  conductor  as 
copper,  and  sometimes  it  is  a  very  poor  conductor. 
The  result  is  that  most  switches  are  too  small  for 
the  currents  which  they  are  intended  to  carry.  Heat- 
ing is  always  a  sure  indication  of  poor  material, 
insufficient  surface  or  poor  workmanship;  or  a  com- 
bination of  these  defects.  A  "jackknife"  switch 
is  the  name  applied  to  the  form  of  switch  which  is 
almost  universally  used  where  snap  switches  are  not 
required.  The  form  is  suggested  by  the  name,  the 
switch  being  designed  so  that  the  blade  or  metal  strip 
which  closes  the  circuit,  shuts  into  the  contacts  in  the 
same  manner  that  the  blade  of  a  jackknife  switch  shuts 
into  the  handle.  These  switches  may  be,  but  usually  are 
not,  equipped  with  springs  to  throw  the  blades.  It  will  be 
readily  seen  that  a  switch  of  this  kind  placed  vertically 
upon  a  wall  will  be  so  arranged  that  the  blade,  when  open, 
will  have  a  tendency  to  fall,  and  this  will  tend  to  close 
the  switch,  if  the  contacts  are  below  the  blade.  If  the 
arrangement  is  reversed  the  weight  of  the  blade  will 
tend  to  keep  the  switch  open.  Sometimes  a  spring  is 
used  to  keep  the  switch  handle  straight  out  from  the 
wall  and  sometimes  the  friction  on  the  joint  in  which 
the  blade  turns  is  sufficient  to  hold  the  blade  in  any 
position  in  which  it  is  placed,  but  since  springs  get 


LOW    POTENTIAL    SYSTEMS.  129 

weak  and  joints  get  loose,  the  best  way  is  to  install  the 
switch  so  that  when  opened  the  blade  will  fall  away 
from  the  contact.  When  thus  installed  the  switch 
cannot  become  closed  by  any  accident  except  the  care- 
lessness of  an  attendant,  or  the  interference  of  some 
meddlesome  person  of  an  investigating  turn  of  mind. 

Fixtures. — Fixtures  are  always  weak  points  in  the 
insulation  of  electrical  wiring  in  a  building.  As  gas 
pipes  are  directly  connected  to  the  ground,  any  defect- 
ive insulation  of  a  circuit  in  a  fixture  immediately 
"grounds"  our  conductor.  To  secure  insulation  there- 
fore we  insulate  our  wire,  insulate  the  conducting  parts 
of  our  sockets  from  the  fixture,  and  then,  as  an  addi- 
tional precaution,  we  insulate  the  fixture  itself  irom  the 
gas  pipe.  We  speak  now  of  what  is  called  a  "  combina- 
tion fixture,"  i.  <?.,  a  fixture  carrying  both  gas  and  elec- 
tric lights.  In  order  to  insulate  the  fixture  itself  and  at 
the  same  time  leave  an  opening  for  the  gas  to  flow  into 
the  pipe  of  the  fixture,  we  use  what  is  known  as  an  insu- 
lating joint.  This  joint  is  inserted  into  the  gas  pipe 
just  below  the  ceiling.  There  are  innumerable  varieties 
of  these  insulating  joints,  some  of  them  pretty  good, 
but  most  of  them  pretty  bad.  They  have  been  made 
with  all  kinds  of  insulation,  hard  rubber,  soft  rubber, 
glass,  leather,  and  everything  else  that  has  ever  been 
used  as  an  insulator.  The  only  rule  to  follow  in  select- 
ing a  joint  is  to  use  one  that  has  been  tested  and 
approved  by  the  underwriters.  As  we  must  insulate  all 
fixtures  from  gas  pipes,  we  must,  of  course,  also  insu- 
late our  conductors  from  the  gas  pipes,  and  must  keep 
them  away  from  them  altogether.  Where  the  gas  pipe 

9 


130  THE    NATIONAL    ELECTRICAL    CODE. 

comes  through  a  wall  or  ceiling  we  place  an  insulating 
joint,  but  between  the  joint  and  the  ivall  or  ceiling  the 
pipe  is  grounded,  we  must  therefore  keep  our  wires 
away  from  this  part  of  the  pipe.  The  shell  referred  to 
in  section  "  b  "  is  the  "canopy"  which  covers  the  hole 
where  the  pipe  comes  through  the  wall  or  ceiling.  This 
canopy  should  be  fastened  to  the  fixture  below  the  insu- 
lating joint,  it  should  be  free  from  the  ceiling  and 
should  be  large  enough  so  that  the  joints  in  the  wires 
inside  can  be  kept  well  away  from  the  uninsulated  part 
of  the  pipe.  It  has  in  the  past  been  quite  a  popular 
practice  to  transform  old  gas  fixtures  into  combination 
fixtures  by  attaching  sockets  to  them  and  running  the 
wires  to  the  sockets  on  the  outside  of  the  fixture.  This 
kind  of  work  was  not  ornamental  at  best,  and  the  efforts 
made  to  prevent  the  appearance  being  very  ugly 
resulted  in  pretty  poor  insulation.  Section  "c"  refers 
to  this  class  of  work.  To  secure  good  insulation  and 
a  neat  appearance  with  this  kind  of  work  is  more 
trouble  and  expense  than,  a  combination  fixture  is 
worth.  The  practice  is  not  now  very  common,  but  a 
fixture  when  wired  this  way  should  be  wired  for  safety 
rather  than  beauty.  Although  in  ordinary  wiring  no 
wire  should  be  used  smaller  than  No.  14  B.  &  S.  or 
1 6  B.  W.  G.  gauge,  it  is  sometimes  necessary  to  use  a 
smaller  wire  in  a  fixture  carrying  a  few  lights,  as  the 
space  for  wire  in  a  fixture  is  often  very  limited.  In 
using  this  fine  wire,  however,  we  should  remember  that 
the  table  of  safe  carrying  capacities  only  allows  a  cur- 
rent of  three  amperes  in  a  No.  18  B.  &  S.  wire.  Section 
"e  "  is  to  prevent  the  mechanical  injury  of  the  insula- 


LOW    POTENTIAL    SYSTEMS.  131 

tion  of  a  wire,  while  it  is  being  drawn  into  a  fixture. 
Section  "f  "  applies  to  an  electric  (not  a  combination) 
fixture,  i.  e. ,  a  fixture  carrying  only  electric  lights.  It  is 
to  protect  the  insulation  from  our  old  enemy  moisture. 
Section  "  g  "  is  for  the  mechanical  protection  of  the 
insulation  of  a  wire,  in  a  combination  fixture.  In  a 
combination  fixture  wires  are  run  between  the  gas  pipe 
and  the  surrounding  ornamental  shell,  as  it  is  the  only 
place  to  run  them  and  have  them  concealed.  It  is  a 
wise  rule,  as  the  practice  of  fixture  manufacturers  has 
been  to  build  a  fixture  so  that  nothing  larger  than  bell 
wire  could  be  hauled  into  it.  All  fixtures  should  be 
thoroughly  tested  in  the  shop  where  they  are  wired,  and 
again  after  they  are  up  in  place  and  before  the  wires  in 
the  fixtures  are  connected  to  the  wires  in  the  building. 
This  second  test  shows  any  injury  to  insulation  that 
may  have  been  caused  in  the  installing  of  the  fixture, 
and  at  the  same  time  shows  whether  the  insulating  joint 
properly  insulates  the  fixture  itself.  When  combination 
fixtures  are  used  they  are  attached  to  the  gas  pipes,  but 
where  simple  electric  fixtures  are  used  they  must  be 
attached  to  some  support  provided  for  that  purpose. 
If  it  were  feasible  it  would  be  well  to  use  an  insulating 
and  fire  proof  material  for  a  support,  but,  in  practice, 
the  fixture  is  usually  supported  from  a  wooden  block, 
which  is  fastened  to  the  ceiling.  When  thus  supported 
the  wires  should  be  treated  as  in  cases  where  they  pass 
through  walls  and  ceilings,  and  be  separated  from  any 
wood-work  by  insulating  and  non  inflammable  bushings. 
Porcelain  tubes  of  convenient  form  and  size  are  the 
best  for  this  purpose 


CHAPTER   XV. 

CLASS    C,     LOW    POTENTIAL    SYSTEMS.        PART    IX. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  28.  ARC 
LIGHTS  ON  Low  POTENTIAL  CIRCUITS: — a.  Must  be  supplied  by 
branch  conductors  not  smaller  than  12  B.  &  S.  gauge,  b.  Must 
be  connected  with  main  conductors  only  through  double  pole  cut- 
outs, c.  Must  only  be  furnished  with  such  resistances  or  regula- 
tors as  are  enclosed  in  non-combustible  material,  such  resistances 
being  treated  as  stoves.  Incandescent  lamps  must  not  be  used 
for  resistance  devices,  d.  Must  be  supplied  with  globes  and  pro- 
tected as  in  the  case  of  arc  lights  on  high  potential  circuits. 

29.  ELECTRIC  GAS  LIGHTING: — Where  electric  gas  lighting  is 
to  be  used  on   the  same  fixture  with  the  electric  light:     a.  No 
part  of  the  gas  piping  or  fixture  shall  be  in  electrical  connection 
with  the  gas  lighting  circuit,     b.   The  wires  used  with  the  fixtures 
must   have   a  non-inflammable   insulation,   or,    where  concealed 
between    the  pipe   and   the   shell    of  the  fixture,    the  insulation 
must  be  such  as  required  for  fixture  wiring  for  the  electric  light. 
c.  The  whole  installation  must  test  free  from  "grounds."    d.  The 
two  installations  must   test  perfectly  free  from  connection  with 
each  other. 

30.  SOCKETS: — a.   No  portion  of  the  lamp  socket  exposed  to 
contact  with  outside  objects  must    be  allowed  to  come  into  elec- 
trical contact  with  either  of  the  conductors,      b.   In  rooms  where 
inflammable  gases  may  exist,  or  where  the  atmosphere  is  damp, 
the  incandescent  lamp  and  socket  should  be  enclosed  in  a  vapor- 
tight  globe. 

31.  FLEXIBLE  CORD: — a.   Must  be  made  of  conductors,  each 
surrounded  with  a  moisture-proof  and  non-inflammable  layer,  and 
further  insulated  from  each   other  by  a  mechanical  separator  of 


LOW    POTENTIAL    SYSTEMS.  133 

carbonized  material.  Each  of  these  conductors  must  be  composed 
of  several  strands,  b.  Must  not  sustain  more  than  one  light  not 
exceeding  50  candle  power,  c.  Must  not  be  used  except  for  pen- 
dants, wiring  of  fixtures  and  portable  lamps  or  motors,  d.  Must 
not  be  used  in  show  windows,  e.  Must  be  protected  by  insulat- 
ing bushings  where  the  cord  enters  the  socket.  The  ends  of  the 
cord  must  be  taped  to  prevent  fraying  of  the  covering,  f.  Must 
be  so  suspended  that  the  entire  weight  of  the  socket  and  lamp 
will  be  borne  by  knots  under  the  bushing  in  the  socket  and  above 
the  point  where  the  cord  comes  through  the  ceiling  block  or 
rosette,  in  order  that  the  strain  may  be  taken  from  the  joints  and 
binding  screws,  g.  Must  be  equipped  with  keyless  sockets  as  far 
as  practicable,  and  be  controlled  by  wall  switches. 

32.  DECORATIVE  SERIES  LAMPS: — Incandescent  lamps  run  in 
series  circuits  shall  not  be  used  for  decorative  purposes  inside  of 
buildings. 

Although  arc  lamps  are  for  the  most  part  operated  in 
series,  and  upon  high  potential  systems,  still  there  is  no 
difficulty  in  operating  them  on  low  potential  systems,  as 
the  ordinary  arc  lamp  requires  only  a  pressure  of  45  to 
50  volts.  Thousands  of  lamps  are  so  operated,  and  the 
practice  is  becoming  daily  more  common.  The  only 
difference  in  the  two  methods  of  operation  is  that, 
when  arc  lamps  are  operated  in  series  on  high  potential 
systems,  a  lamp  is  extinguished  or  cut  out  by  shunting 
the  current,  i.  e.,  connecting  together  the  two  wires 
entering  the  lamp  by  a  low  resistance  path;  while  on  a 
low  potential  system  the  lamp  is  cut  out  or  extinguished 
by  opening  the  circuit  to  the  lamp.  An  ordinary  arc 
lamp  takes  a  current  of  five,  six  or  ten  amperes,  and, 
as  seen  by  the  table  already  given,  the  code  allows  a 
current  of  12  amperes  in  a  No.  14  wire  (B.  &  S.  gauge) 
when  it  is  concealed  and  16  amperes  when  it  is  exposed. 


134  THE    NATIONAL    ELECTRICAL   CODE. 

But  an  arc  lamp  takes  a  larger  current  than  its  normal 
amount  when  it  is  first  started,  and  again  it  is  custom- 
ary to  operate  two  lamps  in  series  on  most  low  poten- 
tial circuits,  so  that  the  code  requires  the  use  of  a  No. 
12  wire  which  is  allowed  to  carry  17  amperes  for  con- 
cealed and  23  amperes  for  open  work.  As  the  two 
lamps  which  are  in  series  are  frequently  located  some 
distance  apart,  it  is  often  cheaper  to  connect  one  wire 
of  the  lamp  circuit  to  the  main  wiring  at  one  point  and 
the  other  wire  at  some  distant  point.  This  kind  of 
construction  leads  to  the  scattering  of  cut-outs  over  a 
plant,  and  is  prohibited  by  section  "b  "  of  Rule  28. 

As  arc  lamps  usually  require  pressure  of  about  50 
volts  each,  and  as  most  incandescent  lamps,  in  isolated 
plants,  are  operated  at  no  volts,  it  is  apparent  that 
when  two  arc  lamps  in  series  are  attached  to  the  same 
circuit  as  incandescent  lamps,  there  is  a  surplus  of 
about  ten  volts  pressure.  In  order  that  the  arc  lamps 
shall  not  get  too  much  pressure,  this  extra  pressure  is 
taken  up  by  inserting  into  the  circuit  to  the  lamps  some 
sort  of  a  resistance,  usually  a  coil  of  German  silver 
wire.  This  resistance  must  be  treated  as  any  other 
resistance  in  a  rheostat  or  resistance  box,  and  must  be 
considered  as  a  source  of  heat  and  enclosed,  so  that  it 
cannot  create  a  hazard,  no  matter  how  hot  it  gets.  The 
use  of  incandescent  lamps  is  prohibited,  as  their  use,  as 
usually  installed,  is  dangerous.  In  order  to  make  a 
resistance  to  carry  5  or  10  amperes  with  incandescent 
lamps,  it  is  necessary  to  use  a  number  of  lamps  in  mul- 
tiple with  one  another,  and  when  one  of  the  lamps 
burns  out,  an  excess  of  current  is  sent  through  the  sur- 


LOW    POTENTIAL    SYSTEMS.  135 

vivors,  and  every  time  a  lamp  gives  out,  a  greater  over- 
load is  thrown  upon  the  remaining  ones.  As  incan- 
descent lamps  are  only  used  in  order  to  make  a  cheap 
resistance,  they  are  seldom  so  placed  that  the  action 
referred  to  will  not  cause  a  hazard.  As  the  action  of 
an  arc  lamp  is  practically  the  same,  no  matter  to  what 
kind  of  a  circuit  it  is  attached,  section  "  d  "  requires 
the  same  safeguards  that  we  have  already  seen  are 
necessary  to  insure  safety  in  arc  lighting. 

Electric  gas  lighting  concerns  the  underwriters  and 
the  engineer  only  as  it  may  interfere  with  the  safety 
of  the  electric  lighting.  Electric  gas  lighting  devices 
are  operated  by  a  few  cells  of  battery  giving  out  a  small 
current  at  a  pressure  of  a  few  (usually  about  three)  volts. 
Where  electric  gas  lighters  are  used  upon  combination 
fixt^lreS)  or  fixtures  carrying  both  gas  and  electric 
lights,  it  is  essential  that  great  care  shall  be  taken. 
We  have  seen  that  the  fixture  itself  must  be  insulated 
from  the  ground  by  an  insulating  joint,  and  it  is  evident 
that  it  is  not  permissible  to  use  any  device  that  will 
destroy  this  insulation.  The  practice  of  using  a  ground 
return  (i.  e.,  using  the  fixture  as  a  part  of  the  battery 
circuit)  is  not  allowable  on  combination  fixtures,  and, 
as  the  battery  wire  may  easily  come  into  contact  with 
the  electric  light  wires,  it  is.  also  necessary  that  they 
shall  have  the  same  grade  of  insulation,  where  both  are 
run  in  the  same  fixture.  These  regulations  are  very 
important  to  secure  safety,  and  they  have  been  called 
forth  by  sad  experience. 

Section  "  a  "  of  Rule  30  is  essential  to  the  safe  main- 
tenance of  a  plant.  Although  a  socket  may  be  attached 


136  THE    NATIONAL    ELECTRICAL   CODE. 

to  a  flexible  cord  and  suspended  in  the  air,  still  there  is 
always  a  chance  that  the  socket  will  be  allowed  to  hang 
or  swing  against  a  gas  pipe  or  something  equally  well 
grounded.  Nearly  every  machine  shop  in  the  country 
is  a  good  example  of  this  fact.  Sockets  should,  there- 
fore, be  designed  to  give  good  insulation,  and  they 
should  also  be  well  made.  This  last  point  is  not  suf- 
ficiently considered,  judging  from  the  sockets  most  seen 
in  the  market.  More  attention  should  be  paid  to  it;  a 
good  socket  is  now  very  cheap,  and  a  poor  socket  is  a 
bad  investment  from  any  point  of  view.  Section  "b  " 
of  the  same  rule  is  to  prevent  an  explosion  from  being 
started  by  an  accidental  arc  in  a  socket  or  lamp.  The 
use  of  an  electric  spark  for  firing  explosives  is  so  famil- 
iar to  every  one  that  the  importance  of  this  regulation 
is  self-evident. 

Flexible  cord  is  what  is  ordinarily  called  "lamp 
cord"  it  consists  of  two  conductors  twisted  together, 
it  is  familiar  to  almost  everyone.  Usually  it  is  cov- 
ered with  green  cotton  braid.  It  has  been  a  weak 
point  in  most  installations.  Where  the  best  of  rubber- 
covered  wires  has  been  used  for  the  wires  on  cleats  or 
knobs  it  has  been  customary  to  use  almost  anything  for 
insulation  of  lamp  cord.  The  reason  is  that  the  cord 
is  usually  in  the  air  where  it  cannot  make  a  "ground;" 
but  the  fact  that  the  cord  is  the  best  kind  of  a  place  to 
get  a  contact  between  two  conductors,  seems  to  have 
been  often  overlooked.  Section  "a."  explains  what 
kind  of  cord  must  be  used.  Section  "b"  limits  the 
use  of  the  cord  to  circuits  for  small  currents  of  not 
over  three  amperes;  as  an  arc,  once  started  between 


LOW    POTENTIAL    SYSTEMS.  137 

the  two  wires  of  a  cord,  will  (if  of  any  strength)  soo.. 
burn  the  cord  in  two,  and  allow  the  lamp  and  perhaps 
allow  some  burning  braid  to  fall  down  upon  the  in- 
flammable material  which  is  usually  at  hand  on  such 
occasions.  Section  "c"  is  aimed  at  the  practice  once 
common,  but  now  prohibited,  of  doing  wiring  with 
cord.  It  is  very  convenient  to  extend  the  wiring  of  an 
existing  plant  by  running  circuits  to  lamps  here  and 
there  with  cord,  fastening  the  cord  in  place  with  sta- 
ples. Miles  of  cord  have  thus  been  run,  and  no  end 
of  trouble  has  been  the  result.  The  insulation  of  all 
cord  is  low.  Even  if  the  insulating  material  is  good, 
the  covering  is  thin  and  will  not  stand  dampness  or 
mechanical  strain.  The  use  of  cord  for  temporary 
work  has  been  extensive.  Unfortunately  it  seems  as  if 
the  most  permanent  thing  in  electrical  work  is  "tem- 
porary construction"  The  same  care  must  be  taken  to 
secure  safety  whether  work  is  permanent  or  if  intended 
to  be  temporary.  The  temptation  to  do  temporary 
work  with  cord  in  show  windows  is  so  great  that  a  spe- 
cial section  is  devoted  to  this  offense.  Show  windows 
are  usually  filled  with  inflammable  material,  they 
have  a  faculty  of  condensing  moisture,  and  a  flexible 
cord  in  a  show  window  is  a  very  handy  thing  to  fasten 
things  to  with  pins.  The  use  of  cord  in  show  windows 
is  one  of  the  things  that  renders  the  life  of  the  elec- 
trical inspector  unhappy;  without  section  "  d  "  it  would 
probably  be  unendurable.  Section  "e"  calls  for  bush- 
ings to  protect  the  cord  from  mechanical  injury,  and 
requires  that  the  ends  of  the  wires  be  taped,  to  prevent 
the  cotton  covering  from  becoming  ignited,  in  case  of 


138  THE    NATIONAL    ELECTRICAL    CODE. 

an  arc  or  flash  in  a  socket.  It  is  customary  to  suspend 
lamps  on  cords  at  a  height  of  six  feet  and  six  inches  from 
the  floor.  The  result  is  that  when  a  person  reaches  up 
to  turn  on  a  lamp,  especially  if  the  person  is  below  the 
average  height,  there  is  a  strain  put  upon  the  cord  and, 
if  the  strain  is  carried  to  the  point  where  the  wires  are 
attached  to  the  socket  or  to  the  ceiling  rosette,  the  con- 
tact is  soon  broken.  The  natural  result  of  such  con- 
struction is,  first,  heating,  and  next  an  arc  at  the  point 
of  contact.  The  code  therefore  requires  that  keyless 
sockets  shall  be  used  as  far  as  practicable,  and  that  in 
all  cases  the  lamp  shall  be  suspended  from  a  knot  in- 
stead of  from  a  joint  or  other  connection  of  the  wire. 
The  decorative  lamps  referred  to  in  Rule  No.  32  are 
what  are  called  "miniature  lamps. "  They  are  mostly 
used  in  decorative  and  often  in  temporary  work.  They 
have  a  low  voltage,  and  therefore  have  to  be  run  in 
series,  to  be  used  on  a  loo-volt  circuit.  Though  of  low 
voltage  they  may  easily  become  a  source  of  danger,  for 
they  usually  take  a  current  of  one  to  one  and  a  half 
amperes,  and,  when  a  circuit  is  broken,  the  pressure 
across  the  break  is  not  that  of  the  lamp,  but  that  of  the 
entire  circuit.  The  miniature  lamps  have  usually  been 
wired  with  very  small  wire,  and  the  sockets  for  attach- 
ing them  to  the  wires  are  flimsy  things,  so  that  they 
have  probably  been  a  source  of  much  trouble;  and  not 
being  a  necessity,  the  underwriters  have  eliminated 
them  as  ordinarily  used  from  inside  construction.  An 
unlimited  number  of  rules  might  be  made  concerning 
details  of  construction,  but  the  rules  of  the  code  are 
only  those  which  seem  absolutely  necessary.  Many  of 


LOW  POTENTIAL  SYSTEMS.  139 

them  may  at  first  glance  seem  severe  or  trivial,  but 
these  very  rules  are  the  ones  that  have  been  originated 
to  prevent  the  continuation  of  practices  which  have 
created  continual  hazards  and  repeated  losses. 


CHAPTER    XVI 

CLASS     D,    ALTERNATING     SYSTEMS.    CONVERTERS    OR 
TRANSFORMERS. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  CLASS  D, 
ALTERNATING  SYSTEMS.  CONVERTERS  OR  TRANSFORMERS.  33. 
CONVERTERS: — a.  Must  not  be  placed  inside  of  any  building, 
except  the  Central  Station,  unless  by  special  permission  of  the 
underwriters  having  jurisdiction,  b.  Must  not  be  placed  in  any 
but  metallic  or  other  non-combustible  cases.  c.  Must  not  be 
attached  to  the  outside  walls  of  buildings,  unless  separated  there- 
from by  substantial  insulating  supports. 

34.  In  those  cases  where  it  may  not  be  possible  to  exclude  the 
converters  and  primary  wires  entirely  from  the  building,  the  fol- 
lowing precautions  must  be  strictly  observed:     Converters  must 
be  located  at  a  point  as  near  as  possible  to  that  at  which  the  pri- 
mary wires  enter  the  building,  and  must  be  placed  in  a  room  or 
vault  constructed  of,  or  lined  with,    fire-resisting  material,   and 
used  only  for  the  purpose.     They  must  be  effectually  insulated 
from  the  ground,  and  the  room  in  which  they  are  placed  be  prac- 
tically air-tight,  except  that  it  shall  be  thoroughly  ventilated  to 
the  out-door  air,  if  possible  through  a  chimney  or  flue. 

35.  PRIMARY  CONDUCTORS: — a.   Must  each  be  heavily  insulated 
with  a   coating   of    moisture-proof   material   from    the   point   of 
entrance  to  the  transformer,  and,  in  addition,  must  be  so  covered 
and  protected   that  mechanical  injury  to  them,  or  contact  with 
them,  shall  be  practically  impossible,  b.   Must  each  be  furnished, 
if  within  a  building,  with  a  switch  and  a  fusible  cut-out  where  the 
wires  enter  the  building,  or  where  they  leave  the  main  line,  on 
the  pole  or  in  the  conduit.     These  switches  should  be  inclosed  in 

(  140) 


ALTERNATING    SYSTEMS.  14! 

secure  and  fire-proof  boxes  perfectly  outside  the  building,  c. 
Must  be  kept  apart  at  least  ten  inches,  and  at  the  same  distance 
from  all  other  conducting  bodies  when  inside  a  building. 

36.  SECONDARY  CONDUCTORS: — Must  be  installed  according  to 
the  rules  for  "Low  Potential  Systems." 

Thus  far  electric  currents  have  been  described  only 
as  being  analogous  to  currents  of  water  flowing  in  a 
pipe.  We  have  however  in  electricity  to  deal  with  two 
kinds  of  currents,  "direct"  currents  and  "alternating^ 
currents.  A  direct  current  may  be  compared  to  a  cur- 
rent of  water  flowing  constantly  in  one  direction  in  a 
pipe.  An  alternating  current  is  one  which  flows  first  in 
one  direction  and  then  in  the  opposite  direction.  We 
may  form  a  conception  of  this  action  by  imagining  that 
we  have  a  cylinder  like  a  steam  engine  cylinder  with  a 
piston  in  it.  Suppose  now  that  we  bore  a  hole  in  one 
end  of  the  cylinder  and  insert  one  end  of  the  pipe  in 
this  hole  and  that  we  then  lead  our  pipe  around  and 
insert  the  other  end  in  a  hole  in  the  other  end  of  the 
cylinder.  Suppose  also  our  cylinder  and  pipe  are 
both  full  of  water.  If  now  we  push  the  piston  forward 
we  will  force  the  water  from  one  end  of  the  cylinder 
into  our  pipe  and  back  into  the  other  end  of  the  cylin- 
der. If  we  reverse  the  motion  of  the  piston  we  will 
cause  the  water  to  flow  back  through  the  pipe  in  the 
reverse  direction.  By  pushing  the  piston  back  and 
forth,  we  can  thus  make  the  current  of  the  water  flow 
alternately  in  one  direction  and  the  other  in  the  pipe. 
This  illustration  will  serve  well  enough  for  our  present 
purpose  to  illustrate  the  difference  between  an  alternat- 
ing and  direct  current  in  electricity.  In  the  case  of  an 
alternating  current  of  electricity  we  have  a  pressure  or 


142  THE    NATIONAL    ELECTRICAL    CODE. 

E.  M.  F.  acting  along  the  wire  first  in  one  direction 
and  then  in  the  opposite  direction  and  this  pressure 
causes  a  flow  of  electricity  or  an  electrical  current  first 
in  one  and  then  in  a  reverse  direction.  These  reversals 
or  alternations  may  take  place  very  frequently.  In 
ordinary  alternating  currents  for  electric  lighting,  the 
current  alternates  or  changes  its  direction  from  seven 
thousand  to  fifteen  thousand  times  a  minute  according 
to  the  speed  and  design  of  the  dynamo.  For  most  appli- 
cations of  electricity,  it  is  best  to  use  a  direct  current, 
as  the  laws  governing  the  action  of  direct  currents  are 
very  simple  and  thoroughly  understood  and"  machines 
for  generating  direct  currents  of  electricity  and  for  con- 
verting them  into  power  have  reached  a  high  degree  of 
perfection.  There  are  however  many  applications  of 
electricity  for  which  alternating  currents  possess  special 
advantages 

Before  we  can  obtain  a  clear  idea  of  the  object  of 
using  an  alternating  current,  we  must  not  only  form  an 
idea  of  electricity  as  a  kind  of  motion  which  we  can 
call  a  current,  but  we  must  consider  it  as  a  mode  of 
transmitting  energy.  We  transform  the  energy  stored 
up  in  coal  into  energy  stored  up  in  steam.  Then 
we  lead  the  steam  into  an  engine  and  transform 
the  energy  in  the  steam  into  energy  in  the  form  of  me- 
chanical motion.  This  energy  in  turn  is  applied  to 
our  dynamo  and  there  transformed  into  electrical  en- 
ergy. Next  the  energy  in  the  form  of  electricity  is 
transmitted  along  a  wire  to  some  point  of  application, 
as  for  example  an  incandescent  lamp,  and  there  it  is 
again  transformed  into  energy  in  the  form  of  heat  and 


ALTERNATING    SYSTEMS.  143 

light.  When  our  energy  is  stored  up  in  steam  we  can 
measure  the  power  given  to  our  engine  in  terms  of  the 
volume  and  pressure  of  the  steam.  The  greater  the 
flow  of  steam  to  the  engine,  and  the  greater  the  pres- 
sure of  the  steam,  the  greater  the  horse  power  trans- 
mitted. In  a  similar  manner  we  can  measure  the 
energy  given  out  by  a  dynamo  to  our  circuit.  The 
greater  the  pressure  or  E.  M.  F.  and  the  greater  the 
current,  the  greater  is  the  power  given  out.  In  fact, 
the  rate  at  which  work  is  done  by  electricity  is  not  only 
proportionate  to  the  pressure  and  to  the  current,  but 
it  is  in  electrical  units  exactly  equal  to  the  pressure 
multiplied  by  the  current.  We  have  seen  that  the  unit 
of  pressure  is  the  volt  and  the  unit  of  the  current  is  the 
ampere.  The  unit  of  the  electrical  power  is  the  watt. 
The  rate  at  which  the  energy  is  being  given  out  to 
a  circuit  is  equal  to  the  amperes  multiplied  by  the  volts, 
and  it  is  expressed  in  watts.  For  example:  an  ordinary 
sixteen  candle  power  lamp  requires  a  current  of  say 
one-half  an  ampere  and  a  pressure  of  100  volts.  The 
power  consumed  would  be  one-half  multiplied  by  100 
or  50  watts.  In  electricity,  as  in  steam,  we  can  get  the 
same  power  by  using  a  high  or  a  low  pressure,  but  if  we 
raise  the  pressure  of  the  steam  we  can  get  our  work 
with  less  steam,  and  if  we  lower  the  pressure  we  must 
use  more  steam  to  get  the  same  amount  of  work.  Just 
so  with  electricity.  We  can  get  a  given  amount  of 
electrical  work  from  a  dynamo  giving  a  small  current 
with  a  high  pressure  or  a  large  current  at  a  low  pres- 
sure, provided  we  increase  the  current  as  we  decrease 
the  pressure  and  decrease  the  current  as  we  increase 


144  THE    NATIONAL    ELECTRICAL    CODE. 

the  pressure  so  that  the  product  of  the  two  (or  the 
watts)  remains  the  same.  For  example,  we  may  operate 
a  sixteen-candle  power  lamp  with  100  volts  and  one- 
half  an  ampere,  or  we  may  by  using  a  suitable  lamp 
get  the  same  candle  power  with  the  same  amount  of  elec- 
trical power  by  operating  at  50  volts  and  one  ampere. 
The  electrical  pressure  used  for  any  particular  kind  of 
work  depends  upon  circumstances.  We  have  seen  that 
in  transmitting  electricity  over  a  conductor  the  thinner 
and  the  longer  the  wire  the  greater  will  be  the  loss  with 
a  given  current;  and  again  we  have  seen  that  for  a 
given  size  and  length  of  wire,  the  greater  the  current 
the  greater  will  be  the  loss.  We  have  just  seen  that 
the  current  required  to  transmit  a  given  amount  of 
electrical  energy  depends  upon  the  pressure  at  which  it 
is  delivered,  and  that  we  can  decrease  the  current  in 
proportion  as  we  increase  the  pressure.  It  follows, 
therefore,  that  if  we  wish  to  transmit  electricity  to  a 
distance  with  a  small  loss  we  can  do  it  in  two  ways: 
First,  we  can  use  a  very  thick  wire;  and,  second,  we 
can  use  a  high  pressure  (and  a  correspondingly  small 
current).  To  appreciate  the  above  statement  we  have 
only  to  remember  that  the  loss  of  energy  is  proportion- 
ate to  the  current  (not  to  the  pressure),  and  that  the 
greater  the  pressure  used  the  smaller  will  be  the  current 
required  to  do  a  given  amount  of  work  or  operate  a 
given  number  of  lamps.  In  steam  work  we  are  limited 
in  the  pressures  we  can  use  for  the  strength  of  our  boilers, 
In  electricity  we  are  limited  in  our  pressures  by  our 
insulating  materials.  The  higher  the  pressure  the 
greater  the  strain  on  the  insulation.  With  high  pres- 


ALTERNATING    SYSTEMS.  145 

sure  the  insulation  becomes  expensive,  and  above  a 
certain  point  it  is  practically  impossible  to  maintain 
any  insulation  at  all.  When  our  wires  are  strung  in  the 
air  upon  glass  insulators  on  wooden  poles,  we  can 
sometimes  go  as  high  as  ten  thousand,  or  even  twenty 
thousand  volts.  Inside  buildings,  however,  such  pres- 
sures are  not  permissible,  as  it  is  practically  impossible 
to  insulate  for  them.  In  inside  wiring  for  incandescent 
lighting  the  pressure  is  limited  by  the  nature  of  our 
incandescent  lamps.  No  one  has  as  yet  been  able  to 
produce  an  incandescent  lamp  that  will  operate  satis- 
factorily and  economically  at  an  E.  M.  F.  of  more  than 
about  115  volts,  and  no  volts  is  the  limit  usually  set. 
This  means  a  pressure  of  no  volts  on  our  inside  wires 
when  we  use  a  two-wire  system,  and  of  220  volts  when  we 
use  a  three-wire  system.  The  advantage  of  the  alternat- 
ing current  in  electrical  engineering,  especially  in  electric 
lighting,  is  that  its  use  enables  us  to  operate  our  lamps  at 
a  low  pressure,  of  say  50  or  100  volts,  and  at  the  same 
time  use  a  high  pressure  on  our  long  outside  lines,  thus 
saving  immensely  in  the  amount  of  copper  required. 

This  is  accomplished  by  the  use  of  what  are  called 
"transformers"  or  "converters."  The  transformer  may 
be  denned  as  a  device  which  transforms  a  small  high 
pressure  current  into  a  large  low  pressure  current,  or 
vice  versa.  The  construction  of  a  transformer  is  sim- 
ple. It  consists  of  a  core  of  soft  iron  wire  or  sheet 
iron  wound  with  two  independent  coils  of  insulated 
copper  wire.  When  an  alternating  current  is  sent 
through  one  of  the  coils  of  the  transformer,  an  E.  M. 
F.  is  set  up  in  the  second  coil,  and  if  the  two  ends  of 


146  THE    NATIONAL    ELECTRICAL    CODE. 

the  second  coil  are  connected  through  a  lighting  cir- 
cuit, or  other  low  resistance,  a  current  will  flow  through 
the  circuit  or  lamps.  The  current  flowing  in  one  coil 
therefore  sets  up  (by  an  action  called  "induction")  a 
current  in  the  second  coil,  although  this  coil  is  indepen- 
dent of  and  insulated  from  the  first,  and  the  current 
will  flow  in  the  second  coil  as  long  as  one  flows  in  the 
first.  If  the  two  coils  have  the  same  number  of  turns 
of  wire  each,  the  current  induced  from  the  second  coil 
will  have  the  same  E.  M.  F.  as  the  current  in  the  induc- 
ing coil,  and,  as  there  is  but  little  loss  in  the  transfor- 
mation (in  a  good  transformer),  the  two  currents  will 
be  about  equal  in  strength.  We  call  the  coil  carrying 
the  inducing  current  the  primary  coil  and  the  one  car- 
rying the  induced  current  the  secondary  coil.  The 
circuit  by  which  the  current  is  led  to  the  primary  coil 
is  called  the  " primary  circuit,"  and  the  circuit  by 
which  the  current  is  led  from  the  secondary  coil  to  the 
lamps  is  called  the  ' '  secondary  circuit. "  In  ordinary 
lighting  the  primary  circuit  is  a  "high  potential"  cir- 
cuit and  the  secondary  circuit  is  a  "  low  potential"  cir- 
cuit. If  we  have  twice  as  many  turns  on  the  primary 
coil  of  the  transformer  as  on  the  secondary  coil,  the 
pressure  in  the  secondary  circuit  will  be  one-half  of 
that  of  the  primary  circuit  and  the  current  will  be  twice 
that  of  the  primary  circuit.  If  our  primary  coil  has 
ten  times  as  many  turns  as  our  secondary  coil,  the 
pressure  on  the  secondary  circuit  will  be  one-tenth  of 
that  on  the  primary  circuit,  and  the  current  will  be  ten 
times  that  in  the  primary  circuit,  and  so  on  for  any 
ratio  of  winding.  The  above  statement  neglects  the 


ALTERNATING    SYSTEMS.  147 

losses  of  transformation,  which  need  not  be  here  con- 
sidered, except  to  state  that  whatever  loss  there  is,  is 
transformed  into  heat  and  raises  the  temperature  of  the 
transformer.  Naturally  the  primary  coil,  having  many 
turns  and  carrying  a  small  current,  is  wound  with  fine 
wire,  and  the  secondary  coil  of  a  few  turns  and  carry- 
ing a  strong  current  is  wound  with  coarse  wire.  As 
commonly  constructed,  a  transformer  is  wound  for  an 
inducing  or  primary  current  of  one  thousand  or  two 
thousand  volts  and  an  induced  or  secondary  current 
for  50  or  100  volts.  One  example  illustrates  the  advan- 
tages of  using  an  alternating  system  when  our  central 
station  is  at  a  distance  from  the  lamps.  Suppose  that  we 
have  200  sixteen-candle-power  lamps  of  loo-volts  inside 
a  building,  we  will  install  a  200  light  transformer.  The 
current  given  out  to  the  secondary  circuit  at  100  volts 
will  be  100  amperes.  If  our  transformer  transforms 
from  1,000  to  100  volts,  we  will  then  have  a  current  of 
but  ten  amperes  in  the  primary  circuit.  The  current  in 
our  outside  circuit  will  therefore  be  but  one-tenth  of 
what  it  would  be  if  we  transmitted  the  current  from  the 
station  at  100  volts.  For  a  given  distance  and  given 
loss  of  energy  in  our  conductors  we  may  therefore  use 
a  wire  for  our  street  circuit  of  only  roo  the  size  (or 
weight  per  mile)  that  would  be  required  if  we  had  to 
tran  mit  at  100  volts.  If  we  use  a  transformer  with  a 
2,000  volt  primary,  the  primary  current  will  be  but  five 
amperes,  and  we  can  transmit  the  same  amount  of 
energy  the  same  distance  and  with  the  same  loss  upon  a 
wire  of  only  ^  the  size  required  for  transmitting  at  100 
volts.  The  saving-  in  copper  is  therefore  enormous. 


148  THE    NATIONAL    ELECTRICAL    CODE. 

The  coils  in  a  converter  or  transformer  are  at  pres- 
ent always  surrounded  by  some  insulating  but  inflamma- 
ble material.  The  wires  are  usually  covered  with  cot- 
ton and  further  insulated  from  one  another,  from  the 
core  and  from  the  iron  case  in  which  they  are  placed, 
by  other  insulating  substances,  oil,  paper,  pitch,  shel- 
lac, fibre,  mica,  etc.,  being  most  commonly  used. 
Rules  Nos.  33,  34  and  35  of  section  "d"  are  self- 
explanatory.  They  simply  require  that  the  transform- 
ers shall  be  inclosed  in  fire  proof  cases  and  shall  be  so 
placed  that  the  inflammable  material  used  in  their  con- 
struction cannot,  even  if  ignited,  create  a  hazard;  and 
that  the  primary  circuit  both  inside  and  outside  the 
transformer  shall  be  absolutely  insulated  from  both  the 
secondary  circuit  and  the  earth.  The  pressures  gener- 
ally used  on  primary  circuits  are  high  enough  to  cause 
instant  death  to  any  one  who  may  be  unfortunate 
enough  to  allow  his  body  to  form  a  part  of  the  circuit, 
and  the  necessity  of  insulating  such  circuits  within 
buildings,  and  especially  of  insulating  them  from  low 
pressure  lamp  circuits,  is  too  apparent  to  require  expla- 
nation. Without  such  insulation  no  one  could  touch  an 
electric  lamp  or  lamp  socket  without  risking  his  life,  and 
the  danger  to  property  would  be  nearly  as  great  as  the 
danger  to  life,  for  the  insulation  allowable  upon  a  low 
tension  circuit  offers  little  or  no  protection  if  submitted 
to  a  strain  of  1,000  to  2,000  volts.  A  converter  is  said 
to  burn  out  when  the  insulating  material  surrounding 
the  coils  is  destroyed  by  heat.  If  properly  constructed 
and  installed,  a  converter  may  burn  out  without  setting 
a  fire,  but  as  the  burning  out  of  the  converter  (espe- 


ALTERNATING    SYSTEMS.  149 

cially  if  filled  with  oil)  may  cause  a  dense  smoke,  con- 
verters should  if  possible  be  placed  outside  of  buildings. 
Where  it  is  absolutely  necessary  to  install  converters  in 
building,  as  for  example  where  the  street  mains  are 
underground,  the  converters  should  be  so  installed  that 
no  damage  from  smoke  will  ensue  even  if  they  are 
burned  out. 

Rule  36  simply  requires  that  secondary  or  lamp  cir- 
cuits shall  be  insulated  and  protected  in  the  same  man- 
ner as  any  other  low  tension  circuits.  The  code  makes 
no  distinction  between  systems  using  alternating  and 
direct  currents.  It  simply  requires  insulation  and  safe 
guards  suited  to  the  pressure.  Now  that  electricity  is 
being  distributed  on  primary  circuits  at  pressures  some- 
times as  high  as  five  thousand  and  ten  thousand  volts, 
the  question  of  insulating  primary  from  secondary  cir- 
cuits is  one  which  will  force  itself  more  and  more  upon 
the  attention  of  the  underwriters.  The  hazard  to  life 
already  demands  a  standard  even  higher  than  that 
required  by  the  code. 


CHAPTER    XVII. 

CLASS    E,     ELECTRIC    RAILWAYS. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  CLASS  E. 
ELECTRIC  RAILWAYS: — 37.  All  rules  pertaining  to  arc  light  wires 
and  stations  shall  apply  (so  far  as  possible)  to  street  railway  power 
stations  and  their  conductors  in  connection  with  them. 

38.  POWER  STATIONS: — Must  be  equipped  in  each  circuit  as  it 
leaves   the  station   with   an  approved  automatic   "breaker,"  or 
other  devices  that  will  immediately  cut  off  the  current  in  case  the 
trolley  wires  become  grounded.    This  device  must  be  mounted  on 
a  fire-proof  base,  and  in  full  view  and  reach  of  the  attendant. 
Automatic  circuit  breakers  should  be   submitted   for   approval 
before  being  used. 

39.  TROLLEY  WIRES: — a.     Must  be  no  smaller  than  No.  o,  B. 
&  S.  copper  or  No.  4,  B.  &  S.  silicon  bronze,    and  must  readily 
stand  the  strain  upon  them  when  in  use.     b.   Must  be  well  insu- 
lated from  their  supports,  and  in  case  of  the  side  or  double  pole 
construction,  the  supports  shall  also  be  insulated  from  the  poles 
immediately  outside   the   trolley  wire.      c.   Must  be  capable  of 
being  disconnected  at  the  power  house,  or  of  being  divided  into 
sections,  so  that  in  case  of  fire  on  the  railway  route  the  current 
may  be  shut  off  from  the  particular  section  and  not  interfere  with 
the  work  of   the  firemen.      This  rule  also  applies   to  feeders, 
d.   Must  be  safely  protected  against  contact  with  all  other  con- 
ductors. 

40.  CAR  WIRING: — Must  be  always  run  out  of  reach  of  the 
passengers,  and  must  be  insulated  with  a  water-proof  insulation. 

41.  LIGHTING  AND  POWER  FROM   RAILWAY  WIRES: — Must  not 
be  permitted  under  any  pretense,  in  the  same  circuit  with  trolley 
wires  with  a  ground  return,  nor  shall   the  same  dynamo  be  used 

(150) 


ELECTRIC    RAILWAYS.  151 

for  both  purposes,   except    in   street    railway   cars,   electric  car 
houses,  and  their  power  stations. 

42.  CAR  HOUSES: — Must  have   special  cut-outs  located  at  a 
proper  distance  outside,  so  that  all  circuits  within  car  houses  can 
be  cut  out  at  any  point. 

43.  GROUND  RETURN  WIRES:— Where  ground  return  is  used 
it  must  be  so  arranged   that  no  difference  of  potential  will  exist 
greater  than  five  volts  to  50  feet,  or  50  volts  to  the  mile  between 
any  two  points  in  the  earth  or  pipes  therein. 

In  this  country  electric  railways  are  almost  without 
exception  operated  at  a  pressure  of  about  500  volts. 
Where  there  are  excessive  losses  in  the  conductors,  the 
dynamo  voltage  is  sometimes  run  up  as  high  as  600  or 
700  volts  in  order  to  give  about  500  volts  to  distant 
points  on  the  system,  but  we  may  say  that  it  is  univer- 
sal practice  to  operate  street  railway  motors  at  from 
500  to  550  volts.  Electric  railway  circuits,  therefore, 
come  under  the  class  of  high  potential  circuits  referred 
to  in  the  code.  For  this  reason,  Rule  No.  37  requires 
substantially  the  same  class  of  construction  in  street 
railway  stations  as  in  arc  light  stations,  "as  far  as 
possible."  The  rules  concerning  central  stations  light 
and  power  (Class  A)  all  apply  to  street  railway  stations 
except  Rule  7,  concerning  "testing."  With  but  few 
recent  exceptions,  all  electric  railways  in  the  United 
States  are  constructed  with  what  is  called  a  "ground 
return,"/,  e.,  the  current  for  operating  the  motor  flows 
from  one  bus  bar  in  the  station  out  on  to  a  system  of 
conductors.  From  these  conductors  it  flows  through 
the  motor,  then  is  led  through  the  axles  and  wheels  of 
the  car  and  rails,  which  form  a  path  by  which  it  returns 
to  the  station.  As  the  rails  are  laid  in  the  earth,  it 


152  THE    NATIONAL    ELECTRICAL    CODE. 

follows  that  one  side  of  the  system  is  grounded.  We 
speak  of  a  "ground  return,"  but  the  current  may  be,  and 
often  is,  led  out  on  the  rails  and  back  upon  the  over- 
hanging conductor.  The  direction  of  the  current  has  no 
bearing  upon  the  manner  of  installing  the  system.  It 
is  evident  that  such  a  system  is  not  insulated  in  the 
ordinary  sense  of  the  term.  The  only  insulation 
required  is  that  necessary  to  prevent  the  current 
from  flowing  from  the  wires  to  the  ground  without 
passing  through  the  motors,  and  to  prevent  the  leakage 
of  current  to  the  conductors  of  other  electric  systems. , 
The  automatic  "breaker"  referred  to  in  Rule  38  is 
what  is  ordinarily  called  a  "  circuit  breaker."  A  circuit 
breaker  is  in  fact  an  automatic  switch  which  opens  the 
circuit  leading  out  of  the  station  when  the  current 
becomes  great  enough  to  endanger  the  dynamos.  The 
circuit  breaker  performs  the  same  function  as  a  main 
line  fuse  in  an  incandescent  lighting  circuit,  but  an 
automatic  switch  is  better  than  a  fuse  for  the  reason 
that  the  overloads  are  frequent  and  heavy.  The  circuit 
breaker  is  more  certain  than  the  fuse;  will  open  in  less 
time  than  is  required  for  a  fuse  to  "blow,"  and  it  can 
be  set  for  any  desired  load  according  to  the  machine  to 
be  protected.  Again,  the  circuit  breaker  can  be  quickly 
re-set,  thus  preventing  annoying  interruption  to  travel. 
The  construction  of  a  circuit  breaker  need  not  be  con- 
sidered here.  From  an  insurance  man's  point  of  view, 
a  circuit  breaker  is  simply  a  safety  device  to  protect  the 
power  house. 

Conductors  of  electric  railways  comprise  the  feeders, 
trolley  wires  and  rails.     The  trolley  wires  are  the  bare 


ELECTRIC    RAILWAYS.  153 

wires  suspended  over  the  middle  of  the  track  from 
which  the  current  is  led  through  the  trolley  to  the  car. 
Feeders  are  the  main  wires  which  conduct  the  current 
from  the  station  to  the  trolley  wire.  Where  the  dis- 
tances are  short  or  the  number  of  cars  small,  the  feeders 
are  sometimes  omitted,  the  current  being  carried  from 
the  station  directly  to  the  trolley  wire.  Where  there  are 
many  cars  or  long  lines,  heavy  feeders  are  used.  The 
rails  complete,  the  circuit  from  the  motors  to  the  power 
house.  They  are  made  into  continuous  conductors  by 
connecting  the  ends  of  adjacent  rails  with  copper  wires 
or  strips  called  "bonds."  Where  the  current  used  is 
very  great,  or  the  distance  very  long,  the  rail  circuit  is 
sometimes  supplemented  either  by  overhead  feeders,  or 
by  a  bare  wire  laid  in  the  ground  alongside  the  rail. 
Such  a  wire  is  called  a  "ground  wire."  Ordinarily  a 
"ground  wire  "  is  not  a  necessity,  but  the  proper  bond- 
ing of  the  rails  is  very  essential.  Section  "a"  Rule 
39,  requires  a  strong  trolley  wire.  This  is  desirable 
from  all  points  of  view.  If  a  trolley  wire  falls  and 
touches  the  ground,  the  current  goes  direct  to  the 
ground,  the  generators  are  overloaded,  the  circuit 
breakers  fly  out  and  the  cars  stopped  until  repairs 
are  made.  Again,  if  the  trolley  wire  falls  upon  a  horse 
or  mule,  the  unfortunate  animal  completes  the  circuit 
and  being  well  grounded  through  iron  shoes,  he  gener- 
ally gets  enough  current  to  electrocute  him.  A  healthy 
man  seems  to  be  tougher  than  a  horse,  but  a  shock  of 
500  or  600  volts  may  under  certain  conditions  seriously 
injure  a  man,  and  if  he  has  a  defective  heart  such  a 
shock  may  permanently  stop  its  operation. 


154  THE    NATIONAL    ELECTRICAL    CODE. 

Section  "  d  "  is  a  regulation  that  is  especially 
demanded  by  insurance  companies.  Many  systems  of 
wiring  in  buildings,  as  for  example  telephone,  telegraph 
and  clock  circuits,  use  ground  returns  and  the  connec- 
tion between  such  wires  and  a  trolley  wire  furnishes  a 
path  to  ground  within  buildings  and  over  conductors 
not  insulated  for  high  pressures  or  large  enough  to 
stand  strong  currents.  Such  connections  or  "crosses" 
have  caused  some  very  serious  fires.  Safety  is  usually 
sought  by  suspending  one  or  more  guard  wires  over 
each  trolley  wire.  The  guard  wires  are  light  iron  wires 
whose  function  it  is  to  support  any  fallen  wires  of  other 
systems  so  that  they  cannot  touch  the  uninsulated  over- 
head railway  conductors.  Car  wiring  comprises  the 
conductor  from  the  trolleys  to  the  motors  and  control- 
ling devices  and  to  the  incandescent  lamps  in  the  car. 
The  preceding  remarks  about  the  pressure  of  street 
railway  circuits  and  the  consequent  danger  from  shocks 
sufficiently  explains  Rule  40. 

Rule  41  refers  to  the  use  of  street  railway  circuits  for 
furnishing  electric  lights  and  power  in  buildings.  This 
use  is  prohibited  except  in  power  houses  and  car  barns. 
There  are  many  obvious  reasons  for  this.  Where  a 
"ground"  return  is  used  it  is  of  course  impossible  to 
insulate  the  conductor  from  the  ground.  One  side  of 
the  system  is  "grounded^"  and  the  other  side  is  sepa- 
rated from  the  ground  by  only  one  thickness  of  insula- 
tion. The  use  of  such  circuits  in  buildings,  is  a  hazard 
to  property  and  a  menace  to  life,  There  are  many 
reasons  why  the  practice  of  using  street  railway  circuits 
for  lighting  and  power  in  buildings  is  bad  and  it  is 


ELECTRIC    RAILWAYS.  155 

absurd  to  allow  such  applications  when  high  insulation 
is  demanded  upon  low  potential  lighting  or  power  cir- 
cuits. Owing  to  the  varying  pressure  on  street  railway 
circuits,  their  use  for  lighting  is  not  often  desirable, 
but  if  it  were  permitted  they  would  be  extensively  used 
for  operating  stationary  motors,  provided  it  was  safe  to 
do  so.  But  it  is  not  safe  except  in  a  few  isolated  excep- 
tional cases,  where  special  precaution  can  be  taken,  as 
for  example  in  a  fire-proof  building  into  which  the  wires 
are  brought  directly  from  street.  In  general  where  there 
is  anything  to  burn,  the  use  of  a  500  volt  grounded  cir- 
cuit is  very  improper. 

Rule  43  has  doubtless  been  called  forth  by  the 
trouble  experienced  by  electrolysis.  •  We  have  spoken 
of  the  current  as  returning  to  the  station  by  way  of  the 
rails,  but  its  path  is  not  necessarily  confined  to  the 
rails.  As  the  rails  are  laid  in  the  ground,  the  earth 
itself  forms  a  return  path  and  in  fact  it  was  once  thought 
desirable  to  depend  on  the  earth  as  a  part  of  the  return 
circuit.  The  current  will  return  along  any  path  that  is 
offered.  If  there  are  iron  waterpipes,  or  gas  pipes  or 
lead  covered  cables  in  the  vicinity  of  the  rails,  a  por- 
tion of  the  current  will  flow  back  on  these  or  along  any 
other  metallic  path.  The  term  "electrolysis,"  as  used 
in  connection  with  street  railway  circuits,  refers  to  an 
action  of  electric  current  similar  to  that  which  takes 
place  when  electricity  is  used  for  electro-plating.  When 
a  current  flows  from  a  rail  to  an  iron  pipe,  then  along 
the  pipe  and  back  to  another  rail,  if  the  rails  and  pipes 
are  in  a  damp  place  electrolysis  will  take  place;  that  is 
to  say,  the  iron  of  the  rails  or  pipe  will  be  rapidly  car- 


156  THE    NATIONAL    ELECTRICAL   CODE. 

ried  off  with  che  current  at  the  point  where  it  leaves  and 
the  rail  or  pipe  will  be  eaten  away,  as  a  metal  plate  is 
eaten  away  in  an  electric  battery  or  in  a  plating  bath. 
The  greater  the  current  the  greater  will  be  the 
amount  of  iron  carried  away  in  a  given  time.  The 
result  of  this  action  is  the  rapid  pitting  and  corrosion 
of  water  and  gas  mains  by  the  current  of  electric  street 
railways  using  a  ground  return.  There  are  two  reme- 
dies for  electrolysis:  First,  we  may  use  an  overhead 
instead  of  a  rail  return  for  the  current.  This  is  very 
expensive  and  not  very  practical,  as  it  requires  twice  as 
many  overhead  wires  and  makes  very  complicated  and 
unsightly  overhead  construction,  especially  crossings 
and  turn-outs.  The  whole  problem  is  too  long  to  dis- 
cuss fully  here.  Electric  railways  may  cause  a  hazard 
by  eating  through  gas  mains  and  igniting  the  gas,  or  by 
destroying  the  insulation  of  underground  electric  cables 
leading  into  buildings. 

Rule  43  is  apparently  an  attempt  to  limit  the  damage 
from  electrolysis.  By  limiting  the  drop  in  volts  (or  the 
loss  in  our  return  circuit)  we  may  decrease  the  danger 
of  the  current  straying  from  rails  to  pipe,  etc.,  and  thus 
lessen  the  danger  of  interference  with  other  systems. 
But,  in  the  light  of  recent  experience,  the  enforcing  of 
Rule  43  would  not  go  far  toward  removing  these  troubles. 
The  loss  of  pressure  (or  difference  of  potential),  allowed 
by  Rule  43,  is  too  great  to  render  the  rule  of  any  value, 
but  it  is  to  be  hoped  that,  at  no  distant  date,  legislation 
or  the  action  of  the  courts  will  demand  some  remedy  that 
will  prevent  the  damage  to  property  which  is  now  going 
on  all  over  the  country. 


CHAPTER    XVIII. 

CLASS    F,     STORAGE    OR    PRIMARY    BATTERIES. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  CLASS  F. 
44.  STORAGE  OR  PRIMARY  BATTERIES:— a.  When  current  for  light 
and  power  is  taken  from  primary  or  secondary  batteries,  the 
same  general  regulations  must  be  observed  as  applied  to  similar 
apparatus  fed  from  dynamo  generators  developing  the  same  dif- 
ference of  potential,  b.  All  secondary  batteries  must  be  mounted 
on  approved  insulators,  c.  Special  attention  is  directed  to  the 
rules  for  rooms  where  acid  fumes  exist,  d.  The  use  of  any 
metal  liable  to  corrosion  must  be  avoided  in  connections  of  sec- 
ondary batteries. 

DEFINITION.  RULE  44.  STORAGE  OR  PRIMARY  BATTERIES: — 
Section  b.  Insulators  for  mounting  secondary  batteries  to  be 
approved  must  be  non-combustible,  such  as  glass,  or  thoroughly 
vitrified  and  glazed  porcelain. 

The  practical  difference  between  a  primary  and  a 
storage  battery  is  pretty  well  indicated  by  the  terms 
"  Storage"  and  "Primary."  A  primary  battery,  like  a 
dynamo,  is  a  source  of  electrical  energy.  In  fact,  it 
can  more  properly  be  called  a  source  of  electrical 
energy  than  a  dynamo,  as  the  current  is  generated  in  a 
primary  battery  without  the  application  of  any  external 
force.  A  storage  battery,  on  the  other  hand,  is  simply 
a  device  by  which  the  electric  energy  generated  in  a 
dynamo  or  primary  battery  is  stored.  The  analogy 
may  be  a  little  far  fetched,  but  we  may  use  our  com- 

157 


158  THE    NATIONAL    ELECTRICAL    CODE. 

parison  between  a  current  of  water  and  a  current  of 
electricity  by  saying  that  a  dynamo  corresponds  to  a 
pump  driven  by  some  prime  mover,  a  primary  battery 
corresponds  to  a  chemical  fire  engine,  which  will  main- 
tain a  flow  of  water  as  long  as  the  supply  of  chemicals 
is  maintained,  and  a  storage  battery  corresponds  to  an 
elevated  tank,  out  of  which  we  can  get  a  flow  of  water 
only  after  it  has  been  filled  up  by  our  pump.  The  dif- 
ference between  a  primary  and  a  secondary  battery 
does  not  have  any  special  bearing  upon  the  rules  con- 
cerning their  installation  and  care,  for  two  reasons: 
first,  a  primary  battery  is  such  an  expensive  source  of 
obtaining  electricity  that  it  is  never  used  for  producing 
electricity  for  light  and  power;  again,  if  primary  bat- 
teries were  so  used  the  rules  regulating  their  installation 
and  use  would  be  the  same  as  for  storage  batteries. 

It  may,  however,  be  of  passing  interest  to  describe  a 
little  more  fully  the  difference  between  the  two  kinds  of 
batteries.  If  we  take  two  plates  of  two  dissimilar  metals 
and  immerse  them  (without  their  coming  into  con- 
tact with  one  another)  in  a  liquid  which  has  a  chemical 
affinity  for  either  one  of  the  metals,  we  have  a  primary 
cell.  If  we  connect  the  two  plates  outside  of  the  liquid 
with  a  wire  or  other  conductor,  an  electric  current  will 
flow  through  the  circuit  thus  formed,  /.  e. ,  it  will  flow 
from  plate  number  one  to  plate  number  two  through 
the  liquid  within  the  cell,  and  from  plate  number  two 
to  plate  number  one  through  the  wire  outside  the  cell. 
The  pressure  or  electro-motive  force  of  the  cell  will 
depend  upon  the  metals  selected  for  the  plates.  For 
any  particular  cell  the  strength  of  current  which  it 


STORAGE    BATTERIES.  159 

gives  out  is  determined  by  the  E.  M.  F.  of  the  cell  and 
the  resistance  of  the  circuit.  The  circuit  is  made  up 
of  three  parts — the  liquid,  the  plates  themselves,  and 
the  external  conductor.  The  length  of  time  that  the 
current  will  be  maintained  depends  upon  the  size 
(t.  e.,  weight)  of  the  plates.  "One  of  the  plates  is 
gradually  eaten  away  by  the  action  of  the  cell.  The 
electrical  energy  in  the  circuit  is  a  reappearance  of  the 
energy  of  chemical  action  in  the  cell,  and  naturally  the 
more  metal  there  is  to  maintain  the  chemical  action 
the  more  electricity  will  be  given  out  before  the  cell  is 
exhausted.  Carbon  may  be  used  instead  of  metal  as 
one  plate,  or  "  electrode"  of  a  cell,  but  the  other  plate 
must  be  of  metal,  and  it  is  the  metal  plate  which  is 
consumed. 

A  "battery,"  strictly  speaking,  is  a  group  of  "cells," 
but  the  words  cell  and  battery  are  used  indiscriminately 
by  nearly  everyone.  We  hear  a  person  speak  of  a  bat- 
tery of  ten  cells,  and  in  the  next  breath  he  speaks  of 
using  ten  cells  of  battery.  The  connection  in  which 
the  words  are  used  generally  leaves  no  doubt  as  to 
whether  one  or  more  cells  is  meant.  One  of  the  most 
common  forms  of  primary  cells  has  plates  of  zinc  and 
carbon,  the  liquid  being  varied  according  to  use  to 
which  the  cell  is  to  be  put.  The  ordinary  well  known 
"gravity  "  or  "blue  stone  "  cell  has  plates  or  electrodes 
of  zinc  and  copper.  In  either  of  these  batteries  it  is 
the  zinc  which  is  consumed,  and  the  more  electricity 
there  is  given  out  the  faster  the  zinc  is  consumed.  The 
poor  economy  of  a  primary  battery  as  compared  with 
a  dynamo  is  apparent  when  we  consider  that  it  requires 


l6o  THE    NATIONAL    ELECTRICAL    CODE, 

a  constant  supply  of  coal  to  keep  up  a  supply  of  elec- 
tricity from  a  dynamo,  and  a  constant  supply  of  zinc 
(and  incidentally  of  chemicals)  to  keep  up  the  supply 
of  electricity  from  a  primary  battery.  As  we  might 
expect,  therefore,  a  primary  battery  is  too  expensive 
for  use  when  much  electricity  is  required,  as  for 
light  and  power.  It  is  cheaper  to  use  an  outfit  that 
burns  coal  than  one  that  burns  zinc.  The  metal  and 
chemicals  required  to  produce  an  electrical  horse-power 
from  the  best  primary  battery  on  the  market  will  cost 
one  hundred  times  as  much  as  the  fuel  required  to  pro- 
duce an  electrical  horse-power  with  a  very  ordinary 
steam  plant  and  dynamo. 

A  storage  battery,  as  its  name  implies,  simply  stores 
up  the  electricity  given  to  it  by  a  dynamo,  and  gives  it 
out  again  when  wanted,  minus  of  course  a- portion 
which  is  lost"  in  this  as  in  all  other  transformations  of 
energy.  This  loss  is  usually  from  five  per  cent,  to 
twenty  per  cent,  of  the  amount  put  into  the  battery,  but 
it  may  be  more  if  the  battery  is  a  poor  one  or  badly 
handled;  fifteen  per  cent,  is  usually  allowed  as  the 
average  loss  with  a  first-class  battery  under  fair  condi- 
tions. We  have  said  that  a  battery  stores  electricity. 
Apparently  it  does,  but  in  reality  it  does  not.  It  does 
store  up  energy  and  gives  it  out  in  \X\zform  of  electricity. 
The  action  is  this:  A  storage  battery,  secondary  bat- 
tery, or  accumulator  (as  it  is  variously  called),  is  much 
the  same  as  any  primary  battery  except  that  the  plates, 
instead  of  being  made  of  two  dissimilar  metals,  are 
made  of  the  same  metal.  All  metals,  however,  will  not 
work  in  a  storage  battery.  All  the  storage  batteries 


STORAGE    BATTERIES.  l6l 

which  have  thus  far  been  enough  of  a  success  to  be  put 
into  practical  use  have  had  plates  of  lead  or  of  a  com- 
bination of  lead  and  oxide  of  lead.  Two  lead  plates 
or  groups  of  plates  immersed  in  any  liquid  will  not 
form  a  primary  battery,  but  if  we  take  two  lead  plates 
and  immerse  them  (without  touching  one  another)  in  a 
dilute  solution  of  sulphuric  acid  and  then  send  an  elec- 
tric current  through  the  combination,  leading  it  into 
one  plate  and  out  of  the  other,  the  action  of  the  cur- 
rent will  in  time  change  the  chemical  condition  of  the 
plates. 

The  current  (which  must  be  a  direct,  not  alternating, 
current)  will  gradually  change  the  plate  by  which  it 
enters  the  cell  into  a  red  oxide  (or  peroxide)  of  lead, 
and  the  other  plate,  or  the  one  by  which  the  current 
leaves  the  cell,  will  be  reduced  to  soft  (or  spongy)  me- 
tallic lead.  When  the  plates  have  reached  this  condi- 
tion, we  have  in  reality  two  plates  of  dissimilar  mate- 
rials, one  of  lead  and  one  of  oxide  of  lead,  and  if  they 
are  now  connected  outside  the  liquid  by  a  wire  or  other 
conductor,  a  current  will  be  given  out  the  same  as  from 
a  primary  battery.  This  current  will  flow  not  as  in  a 
primary  battery  until  one  of  the  plates  is  consumed, 
but  until  both  plates  have  again  undergone  a  chemical 
change  and  are  again  identical  in  their  chemical  com- 
position. To  "form"  a  battery,  /.  e.,  to  get  it  into 
working  condition,  requires  several  charges  and  dis- 
charges, but  we  will  not  encumber  the  present  book 
with  more  detail  or  theory  than  is  necessary  to  give  a 
practical  idea  of  how  the  battery  works.  We  have  seen 
that  in  a  primary  battery  there  is  an  oxidation  which 


1 62  THE    NATIONAL    ELECTRICAL    CODE. 

consumes  the  active  plates,  as  coal  is  consumed  by  oxi- 
dation; in  fact,  there  is  combustion.  In  a  storage  bat- 
tery the  energy  is  not  produced  by  combustion,  but  is 
produced  by  an  outside  source  of  energy.  The  action 
of  repeatedly  charging  and  discharging  a  storage  cell 
is  accompanied  by  a  repeated  oxidizing  and  deoxidiz- 
ing of  the  plates.  A  storage  battery  is  therefore  a  true 
battery.  While  it  practically  stores  electricity,  the  real 
action  is,  first  a  transformation  of  electrical  into  chem- 
ical energy  and  then  a  reverse  action  in  which  chemical 
action  produces  electricity  in  much  the  same  way  as  in 
a  primary  battery. 

We  have  said  that  the  plates  in  a  storage  battery  are 
not  consumed.  This  is  true  only  in  comparison  with 
a  primary  battery.  While  the  plates  after  one  charge 
and  discharge  come  back  to  substantially  their  original 
condition,  continued  charging  and  discharging  eventu- 
ally destroys  the  plates.  The  life  of  the  plates  depends 
upon  how  often  the  battery  is  charged  and  discharged, 
how  long  the  action  is  continued,  and  upon  the  strength 
of  the  charging  and  discharging  current.  An  exces- 
sive current,  either  in  charging  or  discharging,  or  too 
prolonged  a  charge  or  discharge,  even  with  a  moderate 
current,  rapidly  reduces  the  life  of  the  plates.  Stor- 
age batteries  must  be  frequently  examined  and  cleaned, 
and  the  acid  must  be  tested  and  kept  at  proper  specific 
gravity.  Batteries  should  therefore  be  accessible,  and 
should  be  so  placed  that  they  can  be  handled  without  any 
undue  slopping  of  acid,  which  rapidly  turns  woodwork 
into  a  good  conductor.  Section  "b"  of  Rule  44  is 
important.  In  all  storage  battery  plants  inside  build- 


STORAGE    BATTERIES.  163 

ings  the  batteries  should  be  mounted  upon  properly 
designed  oil  insulators.  An  ordinary  porcelain  knob, 
or  even  a  double  petticoat  glass  insulator,  such  as  is 
used  for  supporting  wires  on  poles,  is  of  but  little  use 
for  insulating  a  storage  battery.  A  storage  battery 
(particularly  while  it  is  charging)  gives  off  copious  acid 
fumes,  and  everything  near  a  battery  is  soon  covered 
with  a  film  of  moisture  which  is  an  excellent  conductor. 
As  moisture  condenses  rapidly  on  glass  or  porcelain 
the  ordinary  insulator  soon  fails  to  insulate. 

Section  "c"  of  Rule  44  is  called  forth  by  this  same 
well-known  property  of  a  storage  battery.  The  acid 
fumes  will  corrode  any  metal  except  lead,  so  that 
electrical  machinery  or  instruments  should  not  be 
placed  near  a  battery  unless  the  battery  is  in  a  separate 
room,  or  closet,  which  is  ventilated  into  a  separate 
room,  or,  better,  into  the  open  air 

Section  "d"  practically  prohibits 'the  use  of  any 
metal  for  battery  connections  except  lead.  The  best 
way  to  join  cells  is  to  have  the  plates  provided  with 
long  strips  or  lugs  of  lead,  and  to  make  the  connection 
with  solder,  far  enough  away  from  the  acid  so  that  they 
will  stay  reasonably  dry.  As,  however,  such  a  perma- 
nent connection  might  discourage  the  average  attendant 
from  disconnecting  the  cells  when  necessary  for  inspec- 
tion or  cleaning,  some  kind  of  a  clamp  is  usually 
preferred.  The  device  which  comes  the  nearest  to 
giving  a  satisfactory  joint,  and  at  the  same  time  one 
that  can  be  readily  disconnected,  is  the  lead-covered 
bolt.  The  lead  lugs  are  bolted  together  by  a  short 
brass  bolt  passing  through  holes  in  the  lugs;  this  bolt 


164  THE    NATIONAL    ELECTRICAL    CODE. 

is  threaded  on  both  ends,  and  each  end  is  provided  with 
a  brass,  lead-covered  bolt.  The  result  of  this  arrange- 
ment is  that  when  the  bolts  are  drawn  up  tightly  the 
lugs  are  clamped  together,  and  if  the  joint  is  carefully 
made  and  kept  tight  it  leaves  nothing  but  lead  exposed 
to  the  fumes  of  the  acid.  For  general  use  this  joint 
gives  the  best  results  of  anything  yet  devised  for  the 
purpose. 

A  battery  should  always  be  protected  by  safety 
devices  the  same  as  a  dynamo.  Circuit  breakers  and 
fuses  are  both  used  for  this  purpose. 

Section  "  a  "  of  Rule  44  explains  itself.  It  is  a  rule 
which  has  been  often  neglected  in  the  past  with  disas- 
trous results,  the  battery  itself  usually  being  the  chief 
sufferer.  It  is,  however,  a  rule  that  should  be  rigidly 
enforced. 


CHAPTER    XIX. 

MISCELLANEOUS. 

TEXT  OF  THE  CODE  COVERED  BY  THIS  CHAPTER.  MISCELLA- 
NEOUS:— 45.  a.  The  wiring  in  any  building  must  test  free  from 
grounds;  i.  e.,  each  main  supply  line  and  every  branch  circuit 
shall  have  an  insulation  resistance  of  at  least  25,000  ohms,  and 
should  have  an  insulation  resistance  between  conductors  and 
between  all  conductors  and  the  ground  (not  including  attach- 
ments, sockets,  receptacles,  etc.,)  of  not  less  than  the  following: 

Up  to      10  amperes 4,000,000 

25         "       1,600,000 

50         "        800,  ooo 

100         " 300,000 

200         "       160,000 

400         "       : 80,000 

"        800         "       22,000 

"     1,600         "       11,000 

All  cut-outs  and  safety  devices  in  place  in  -the  above.  Where 
lamp  sockets,  receptacles,  and  electroliers,  etc.,  are  connected, 
one-half  of  the  above  will  be  required,  b.  Ground  wires  for  light- 
ning arresters  of  all  classes,  and  ground  detectors,  must  not  be 
attached  to  gas  pipes  within  the  building,  c.  Where  telephone, 
telegraph  or  other  wires  connected  with  outside  circuits  are 
bunched  together  within  any  building,  or  where  inside  wires  are 
laid  in  conduit  or  duct  with  electric  light  or  power  wires,  the  cov- 
ering of  such  wires  must  be  fire-resisting,  or  else  the  wires  must 
be  inclosed  in  an  air-tight  tube  or  duct.  d.  All  conductors  con- 
necting with  telephone,  district  messenger,  burglar-alarm,  water- 
clock,  electric  time,  and  other  similar  instruments,  must  be  pro- 
vided near  the  point  of  entrance  to  the  building  with  some  protec- 

(165) 


1 66  THE    NATIONAL    ELECTRICAL    CODE. 

tive  device  which  will  operate  to  shunt  the  instruments  in  case  of 
a  dangerous  rise  of  potential,  and  will  open  the  circuit  and  arrest 
an  abnormal  current  flow.  Any  conductor  normally  forming  an 
innocuous  circuit  may  become  a  source  of  fire-hazard  if  crossed 
with  another  conductor,  through  which  it  may  become  charged 
with  a  relatively  high  pressure.  (See  Definitions.)  The  follow- 
ing formula  for  soldering  fluid  is  suggested: 

Saturated  solution  of  zinc 5  parts 

Alcohol .4  parts 

Glycerine i  part 

DEFINITIONS.  RULE  45.  WIRE  PROTECTORS:— Protectors  must 
have  a  non-combustible,  insulating  base,  and  the  cover  to  be  pro- 
vided with  a  lock  similar  to  the  lock  now  placed  on  telephone 
apparatus  or  some  equally  secure  fastening,  and  to  be  installed 
under  the  following  requirements:  i.  The  protector  to  be  located 
at  the  point  where  the  wires  enter  the  building,  either  immedi- 
ately inside  or  outside  of  the  same.  If  outside,  the  protector  to 
be  inclosed  in  a  metallic  waterproof  case.  2.  If  the  protector  is 
placed  inside  of  building,  the  wires  of  the  circuit  from  the  support 
outside  to  the  binding  posts  of  the  protector  to  be  of  such  insula- 
tion as  is  approved  for  service  wires  of  electric  light  and  power, 
and  the  holes  through  the  outer  wall  to  be  protected  by  bushing 
the  same  as  required  for  electric  light  and  power  service  wires. 

3.  The  wire  from  the  point  of  entrance  to  the  protector  to  be  run 
in  accordance  with  rules  for  high  potential  wires;  i.  e.,  free  of  con- 
tact with  building,  and  supported  on  non-combustible  insulators. 

4.  The  ground  wire  shall  be  insulated,  not  smaller  than  No.  16  B. 
&  S.  gauge.     This  ground   wire  shall  be  kept  at  least  three  (3) 
inches  from  all  conductors,  and  shall  never  be  secured  by  unin- 
sulated double-pointed  tracks.      5.     The    ground  wire  shall  be 
attached  to  a  water  pipe,  if  possible;  otherwise  may  be  attached 
to  a  gas  pipe.     The  ground  wire  shall  be  carried  to  and  attached 
to  the  pipe  outside  of  the  first  joint  or  coupling  inside  the  founda- 
tion walls,  and  the  connection  shall  be  made  by  soldering,  if  pos- 
sible.    In  the  absence  of  other  good  ground,  the  ground  shall  be 
made  by  means  of  a  metallic  plate  or  a  bunch  of  wires  buried  in 
a  permanently  moist  earth. 


MISCELLANEOUS.  167 

MATERIALS: — The  following  are  given  as  a  list  of  non-combus- 
tible, non-absorptive,  insulating  materials  and  are  listed  here  for 
the  benefit  of  those  who  might  consider  hard  rubber,  fiber,  wood, 
and  the  like,  as  fulfilling  the  above  requirements.  Any  other  sub- 
stance which  it  is  claimed  should  be  accepted,  must  be  forwarded 
for  testing  before  being  put  on  the  market,  i.  Thoroughly  vitri 
fied  and  glazed  porcelain.  2.  Glass.  3.  Slate  without  metal 
veins.  4.  Pure  sheet  mica.  5.  Marble  (filled).  6.  Lava  (cer- 
tain kinds  of).  7.  Alberene  stone 

WIRES: — The  following  list  of  wires  have  been  tested  and  found 
to  comply  with  the  requirements  for  an  approved  insulation  under 
Rule  10  (a),  Rule  12  (d),  and  Rule  18  (a).  Acme;  Ajax;  Ameri- 
canite;  Bishop;  Canvasite;  Clark;  Columbia;  Crescent;  Crown; 
Edison  Machine;  Globe;  Grimshaw  (white  core);  Habirshaw  (red 
core);  Kerite;  National  India  Rubber  Co.  (N.  I.  R.);  Okonite; 
Paranite;  Raven  Core;  Safety  Insulated  (Requa  white  core,  Safety 
black  core);  Salamander  (rubber  covered);  Simplex  (caoutchouc); 
United  States  (General  Electric  Co.)  None  of  the  above  wires  to 
be  used  unless  protected  with  a  substantial  braided  outer  covering. 

We  have  already  seen  that  wires  of  opposite  polarity 
must  be  insulated  from  one  another,  and  that  all  wires 
must  be  insulated  from  the  ground.  The  question  now 
arises:  ' '  What  is  in sulation ?"  The  term  insulation  is 
a  relative  one.  Every  conductor,  even  one  of  copper, 
offers  a  measurable  resistance  to  a  flow  of  current,  and 
every  insulator,  even  rubber,  permits  a  measurable 
amount  of  electricity  to  pass  through  it.  A  wire  cov- 
ered with  a  thin  covering  of  rubber  may  be  well  insu- 
lated to  withstand  a  pressure  of  100  volts,  but  poorly 
insulated  for  a  pressure  of  1,000  volts.  What  then  is 
proper  insulation?  The  insulating  properties  of  the 
various  rubber  compounds  used  to  cover  wire  vary 
very  greatly  when  the  insulation  is  new,  and  much  more 
when  the  insulation  is  old;  the  covering  of  wires  is 


1 68  THE    NATIONAL    ELECTRICAL    CODE. 

often  injured  or  destroyed  by  the  carelessness  of  work- 
men; and,  again,  every  device  attached  to  a  circuit 
offers  some  opportunity  for  leakage.  The  thickness  of 
insulation  on  wires  cannot  therefore  be  taken  as  a 
standard.  The  only  practical  standard  is  an  electrical 
standard.  In  any  system  of  conductors  the  insulation 
of  the  wires  must  present  a  certain  resistance  to  the 
flow  of  current  from  the  positive  to  the  negative  con- 
ductors, along  any  path,  except  the  path  provided  by 
the  wires  themselves  and  the  lamps,  motors,  etc.,  con- 
nected to  them.  This  resistance  is  called  the  insulation 
resistance  of  the  system.  It  is  measured  in  ohms. 

We  must  bear  in  mind  that  our  electricity  does  not 
try  to  leak  off  into  space  or  into  the  ground,  but  that 
whenever  there  is  a  difference  of  electrical  pressure 
between  two  wires,  this  pressure  is  always  trying  to  send 
a  current  from  one  wire  to  the  other.  The  current  which 
will  flow  depends  upon  the  total  resistance  of  all  paths 
between  the  two  wires.  If  the  two  wires  come  into 
metallic  connection,  they  are  as  we  say  ' '  cros sed, "  and 
we  have  what  is  called  a  short  circuit.  If  one  of  the 
wires  comes  into  electrical  contact  with  the  earth,  then 
that  wire  is  "grounded ;"  we  then  have  nothing  sepa- 
rating the  wires  electrically  except  the  insulation  of  the 
other  wire.  If  now  the  second  wire  becomes  connected 
electrically  to  the  earth,  we  have  the  two  wires  con- 
nected electrically  through  the  earth,  and  a  leakage 
takes  place.  The  amount  of  this  leakage  of  course 
depends  upon  the  resistance  of  the  contacts  between 
the  wires  and  the  earth.  A  ground  on  one  wire  is  only 
dangerous  as  it  is  a  step,  half  way,  toward  the  crossing  of 


MISCELLANEOUS.  169 

wires  of  opposite  polarity,  but  when  any  wire  in  a  system 
is  grounded,  a  second  ground  appearing  anywhere  on 
any  wire  of  opposite  polarity,  creates  a  cross  and  a  leak. 
When  the  resistance  between  a  wire  and  the  ground 
is  very  low,  we  say  we  have  a  "  dead  ground,"  and  when 
we  have  a  dead  ground  on  both  poles  of  the  system  we 
have  a  "short  circuit ;"  and  as  a  result,  a  leakage 
which  is  only  limited  by  the  capacity  of  our  dynamos 
and  engines.  The  code  requires  an  insulation  resist- 
ance of  at  least  25,000  ohms  on  any  main  or  branch 
circuit.  This  rule  is  applicable  only  to  the  low  poten- 
tial circuits  used  for  incandescent  lighting.  The  code, 
as  we  have  seen,  defines  low  potential  circuits  as 
those  carrying  a  pressure  of  300  volts  or  less.  This 
insulation,  /.  e.,  25,000  ohms,  is  the  least  that  is  allowed 
on  any  circuit.  Why  this  standard  is  mentioned  in  the 
code  is  not  apparent,  since  in  order  to  get  the  insula- 
tion required  by  the  code  on  any  system  of  conductors, 
the  insulation  on  any  individual  circuit  must  be  much 
better  than  25,000  ohms.  The  more  circuits  there  are 
in  any  system  of  wiring,  the  lower  will  be  the  insulation 
resistance  of  the  system,  supposing  a  given  resistance 
for  each  circuit.  This  is  easily  understood.  If  we 
have  two  wires  of  opposite  polarity,  and  provide  a  path 
for  the  current  to  flow  between  them,  we  will  have  a 
certain  resistance  opposing  the  flow,  whether  the  path 
be  good  or  poor;  whether  it  is  formed  by  a  conductor 
or  an  insulator.  If  now  we  provide  a  second  path  just 
like  the  first,  the  total  resistance  to  the  flow  will  be  but 
one-half  what  it  was  before.  Each  and  every  time  that 
we  add  another  path,  we  lower  the  total  resistance 


1 70  THE    NATIONAL    ELECTRICAL   CODE. 

between  the  wires.  When  we  have  a  number  of  lamps 
or  motors  forming  separate  paths  for  the  current  to  flow 
from  the  positive  to  the  negative  conductors  of  a  sys- 
tem, we  say  that  the  lamps  or  motors  are  in  "  multiple 
arc,"  or  in  "multiple."  With  a  given  pressure,  the 
more  lamps  there  connected  the  less  will  be  the  total 
resistance  of  the  circuit  thus  formed,  and  the  greater 
will  be  the  current.  With  insulation  it  is  the  same. 
Every  foot  of  wire  added  to  a  system  decreases  the 
insulation  resistance  of  the  system  and  increases  the 
leakage  of  current. 

If  we  have  two  circuits,  each  having  an  insulation 
resistance  of  1,000,000  ohms,  their  combined  insulation 
resistance  will  be  500,000  ohms.  If  we  have  ten  such 
circuits,  the  insulation  resistance  of  the  system  will  be 
100,000  ohms,  and  if  we  have  100  such  circuits,  the 
total  insulation  resistance  of  the  system  will  be  but 
10,000  ohms.  With  a  given  kind  of  construction  and 
of  insulation  covering  for  our  wire,  we  can  figure  that 
the  more  wire  there  is  used  in  any  system  of  conduct- 
ors, the  less  will  be  the  insulation  resistance.  It  might 
be  desirable  (if  it  were  possible)  to  have  an  arbitrary 
standard  for  the  insulation  resistance  of  all  plants  using 
a  certain  voltage,  but  it  is  not  possible  to  work  to  such 
a  standard,  for  we  are  limited  on  large  plants  by  the 
quality  of  the  materials  available  for  insulation,  and 
the  adoption  of  such  a  standard  would  be  equivalent  to 
a  lowering  of  the  standard  for  small  plants,  which  is  by 
no  means  desirable,  experience  having  demonstrated 
that  the  best  insulation  that  can  be  obtained  from 
materials  in  the  market  is  none  too  good. 


MISCELLANEOUS.  I  7  I 

It  is  not  feasible  to  make  the  standard  depend  upon 
the  total  length  of  wire  in  a  system,  owing  to  the  diffi- 
culty of  finding  out  this  amount  and  to  the  fact  that 
every  cut-out  and  socket  attached  to  the  system  adds  a 
leakage  point.  The  code,  therefore,  makes  the  insula- 
tion resistance  required  depend  upon  the  number  of 
lamps  connected,  or,  what  is  the  same  thing,  upon  the 
amperes  of  current  in  the  whole  system.  Allowing 
about  ten  amperes  to  a  branch  circuit,  the  table  given 
under  section  "a,"  Rule  45,  corresponds  to  an  average 
insulation  resistance  of  from  about  2,000,000  to  4,000,- 
ooo  ohms  per  circuit,  according  to  the  size  of  the  plant. 
Every  device  attached  to  the  system  lowers  the  insula- 
tion resistance  so  that  the  code  permits  a  resistance  of 
one-half  this  amount  when  the  lamps,  fixtures,  etc.,  are 
in  place.  We  may,  therefore,  say  that  the  standard  of 
the  code  is  1,000,000  to  2,000,000  ohms  per  circuit, 
according  to  the  size  of  the  plant,  if  we  assume  the  cir- 
cuit to  average  ten  amperes  each.  Since  it  is  now 
customary  to  allow  only  ten  to  twelve  lamps  or  five  to 
six  amperes  to  a  branch  circuit,  the  standard  really 
amounts  after  all  to  an  average  of  3,000,000  to  4,000,- 
ooo  ohms  per  circuit.  It  is  pretty  fair  practice  to 
require  1,000,000  ohms  or  one  "megohm"  on  each  and 
every  circuit,  and  a  total  insulation  resistance  on  the 
entire  system  at  least  equal  to  that  called  for  in  the 
code.  If  no  circuit  is  less  than  one  megohm,  many  of 
the  circuits  will  show  several  megohms,  so  that  the 
average  will  be  much  more  than  a  megohm,  and  the 
entire  system  will  test  out  all  right. 

The  requirements  of   Rule  45,    section    "  b,"  have 


172  THE    NATIONAL    ELECTRICAL   CODE. 

been  referred  to  before  in  the  code.  A  gas  pipe  may 
form  a  very  poor  path  for  a  current  to  take  to  the 
earth,  and  if  the  piping  in  the  building  has  been  dis- 
connected from  the  street  mains,  the  pipe  may  not 
provide  any  path  at  all  to  the  earth.  It  is  certainly  poor 
policy  to  provide  a  path  to  conduct  lightning  to  a  net- 
work of  piping  in  a  building  where  there  is  no  assurance 
that  there  is  a  path  jfrww  the  piping  to  the  earth.  Again, 
it  is  obvious  that  we  may  be  inviting  trouble  by  leading 
lightning  and  perhaps  heavy  dynamo  currents  to  a  pipe 
filled  with  gas.  The  object  of  section  "  c  "  of  Rule  45 
is  to  prevent  fires  from  being  caused  by  the  accidental 
crossing  of  electric  light  or  power  wires  with  other 
wires  which  themselves  carry  harmless  currents  (/.  e., 
small  currents  of  very  low  pressure),  and  which  do  not, 
under  normal  conditions,  require  high  insulation.  The 
crossing  of  light  or  power  wires,  either  in  the  street  or 
inside  buildings,  with  telephone,  telegraph,  electric 
clock  wires,  etc.,  may,  if  there  is  no  protecting  device, 
quickly  send  a  current  through  them  that  will  heat  them 
red  hot,  or  even  cause  them  to  melt.  The  wires  used 
for  bells,  electric  clocks,  etc.,  are  commonly  covered 
with  a  cotton  wrapping,  which  is  often  saturated  in 
paraffine,  and  they  are  laid  directly  upon  woodwork. 
Crosses  between  electric  light  and  power  wires  and  wires 
of  the  class  above  referred  to  may  be  and  often  are 
sources  of  greater  hazard  than  crosses  between  electric 
light  or  power  wires.  Even  the  rubber  compounds  used 
to  insulate  wire  are  often  inflammable,  and  the  rules  to 
prevent  the  use  of  insulation  that  will  ignite  and  carry 
flame  should  be  observed  wherever  it  is  possible. 


MISCELLANEOUS.  173 

This  matter  of  inflammable  covering  for  wires  will 
undoubtedly  receive  more  attention  in  the  future  than 
it  has  received  in  the  past,  and  the  time  will  surely 
come  when  all  wires  will  be  of  such  material,  or  so  insu- 
lated, that  they  cannot  carry  flame.  Section  "  d " 
requires  the  use  of  a  device  to  prevent  the  class  of  con- 
ductors, above  referred  to,  from  receiving  from  a  light 
or  power  circuit  a  current  sufficient  to  overheat  them, 
or  from  becoming  alive  from  contact  with  conductors 
of  a  system  having  a  pressure  high  enough  to  be  dan- 
gerous to  life.  The  "protectors"  commonly  used  are 
fusible  cut  outs  having  some  kind  of  fuse  which  will 
open  the  circuit  quickly  upon  the  flow  of  a  small  cur- 
rent. These  devices  are  described  in  the  "Definitions" 
as  completely  as  it  is  possible  to  describe  them  in  this 
brief  work. 

The  securing  of  high  insulation  and  of  maintaining  it 
is  the  great  problem  of  the  constructor.  The  code 
shows  what  is  required;  the  way  to  secure  it  is  to  use 
the  right  material  and  methods  and  good  workmanship 
and  to  test  the  insulation  carefully  during  construction 
and  at  each  stage  of  the  work.  The  code  gives  a  list 
of  wires  that  we  are  permitted  to  use.  These  wires  have 
about  all  grades  of  insulation  on  them  from  the  best  to 
about  the  poorest  that  can  be  sold.  Experience  alone 
determines  what  wire  or  insulating  material  is  good 
enough  for  or  best  adapted  to  each  piece  of  construc- 
tion. In  installing  a  plant  the  insulation  of  each  circuit 
should  be  tested  as  it  is  run  before  anything  is  con- 
nected to  it.  The  wiring  in  the  fixtures  should  be  tested 
before  the  fixtures  are  put  in  place,  and  it  is  well  to  test 


174  THE    NATIONAL    ELECTRICAL    CODE. 

them  again  after  they  are  in  place  but  before  they  are 
connected  to  the  circuit.  Finally  each  and  every  cir- 
cuit should  be  tested  after  everything  is  complete  and 
everything  in  place  except  the  lamps.  In  this  manner 
it  is  easy  to  secure  proper  insulation  provided  proper 
materials  are  used,  and  by  making  periodical  tests  and 
keeping  a  record  of  the  measurements  we  can  always 
tell  the  condition  of  the  insulation  and  can  readily 
maintain  the  required  standard. 


CHAPTER  XX. 

THE  1896  EDITION  OF  THE  CODE. 

Since  Chapter  XIX  was  written  the  code  has  been 
revised,  and  the  revised  edition,  dated  January  ist, 
1 8(^6,  has  been  distributed.  We  would  suggest  that 
those  of  our  readers  who  are  interested  in  watching  the 
evolution  of  the  code  compare  the  code  of  1895  with 
the  code  of  1896  section  by  section.  Such  a  comparison 
made  upon  the  publication  of  each  new  edition  will  be 
a  great  help  to  any  one  who  wishes  to  keep  in  touch 
with  the  electrical  inspectors.  The  code  of  1896  dif- 
fers but  little  from  the  preceding  edition,  and  the 
changes  c.onsist  for  the  most  part  of  the  addition  of 
certain  specific  requirements  to  the  general  require- 
ments of  the  earlier  edition.  In  the  preceding  edition 
the  "Definitions"  which  explained  the  rules  were 
printed  as  an  appendix  at  the  end  of  the  code.  In  the 
present  edition  these  definitions  are  incorporated  into 
and  made  a  part  of  the  rules  themselves,  a  change 
which  will  be  a  great  help  to  those  using  the  code  in 
practical  work  and  to  those  who  wish  to  glance  through 
it  occasionally  to  find  out  what  is  required  for  a  special 
kind  of  construction.  Every  one  who  refers  to  the 
code  should  have  a  copy  of  this  edition.  The  edition 
of  January  ist,  1896,  opens  with  a  page  of  "  General 

(i75) 


176  THE    NATIONAL    ELECTRICAL    CODE. 

Suggestions."  These  suggestions  cover  the  broad  prin- 
ciples of  the  code  to  which  we  have  endeavored  to  call 
special  attention  in  our  articles.  Following  are  the 
suggestions  which  we  believe  will  be  readily  understood 
and  appreciated  by  our  readers  without  comment  on 
our  part,  but  it  should  be  noted  that  they  show  clearly 
how  thoroughly  the  underwriters  appreciate  the  fact 
that  safety  is  to  be  secured  only  by  intelligent  design 
and  careful  and  honest  workmanship: 

GENERAL  SUGGESTIONS: — In  all  electric  work  conductors,  how- 
ever well  insulated,  should  always  be  treated  as  bare,  to  the  end 
that  under  no  conditions,  existing  or  likely  to  exist,  can  a  ground- 
ing or  short  circuit  occur,  and  so  that  all  leakage  from  conductor 
to  conductor,  or  between  conductor  and  ground,  may  be  reduced 
to  the  minimum.  In  all  wiring  special  attention  must  be  paid  to 
the  mechanical  execution  of  the  work.  Careful  and  neat  run- 
ning, connecting,  soldering,  tapping  of  conductors  and  securing 
and  attaching  of  fittings,  are  especially  conducive  to  security  and 
efficiency,  and  will  be  strongly  insisted  on.  In  laying  out  an 
installation  the  work  should,  if  possible,  be  started  from  a  center 
of  distribution,  and  the  switches  and  cut-outs,  controlling  and 
connected  with  the  several  branches,  be  grouped  together  in  a 
safe  and  easily  accessible  place,  where  they  can  be  readily  got  at 
for  attention  or  repairs.  The  load  should  be  divided  as  evenly  as 
possible  among  the  branches,  and  all  complicated  and  unnecessary 
wiring  avoided.  The  use  of  wireways  for  rendering  concealed 
wiring  permanently  accessible  is  most  heartily  endorsed  and 
recommended;  and  this  method  of  accessible  concealed  construc- 
tion is  advised  for  general  use.  Architects  are  urged,  when 
drawing  plans  and  specifications,  to  make  provision  for  the  chan- 
neling and  pocketing  of  buildings  for  electric  light  or  power 
wires,  and  in  specifications  for  electric  gas  lighting  to  require  a 
two-wire  circuit,  whether  the  building  is  to  be  wired  for  electric 
lighting  or  not,  so  that  no  part  of  the  gas  fixtures  or  gas  piping 
be  allowed  to  be  used  for  the  gas-lighting  circuit. 


THE    1896    EDITION    OF    THE    CODE.  177 

We  believe  we  are  justified  in  concluding  from  the 
above  "  Suggestions"  that  what  are  most  needed  in  the 
electric  art  are,  first,  the  use  of  more  brains  in  the 
designing  of  plants  and  systems  of  conductors;  and, 
second,  better  workmanship.  Better  workmanship  can 
be  obtained  by  more  thorough  inspection  and  by  estab- 
lishing some  standard  of  skill  for  workmen  so  that 
intelligent  and  careful  wiremen  shall  be  better  paid, 
and  the  men  who  are  not  mechanics  shall  either  become 
laborers  or  go  into  some  other  line  of  work  where  their 
carelessness  will  not  endanger  the  lives  and  property  of 
others.  As  the  revised  code  contains  no  radical 
changes  we  will  not  review  the  entire  text,  but  will 
simply  call  attention  as  briefly  as  possible  to  the 
changes  that  have  been  made.  We  will  take  these  up 
under  the  various  "Classes"  of  work  in  the  order 
given  in  the  code. 

"  Class  A,  Central  Stations." — Under  Rule  i  "Gen- 
erators," section  "b"  now  reads  : 

b.  Must  be  insulated  on  floors  or  base  frames,  which  must  be 
kept  filled  to  prevent  absorption  of  moisture,  and  also  kept  clean 
and  dry.  Where  frame  insulation  is  impossible,  the  inspector 
may,  in  writing,  permit  its  omission,  in  which  case  the  frame 
must  be  permanently  and  effectively  grounded. 

This  change  is  made  to  allow  and  regulate  the  use  of 
"direct  coupled"  dynamos,  /.  e.,  dynamos  which  are 
coupled  direct  to  an  engine  without  the  use  of  belts  or 
gears,  the  armature  of  the  dynamo  being  mounted 
directly  upon  the  engine  shaft.  An  engine  is  always 
connected  (electrically)  to  the  earth  so  that  it  4s  diffi- 
cult to  insulate  the  frame  of  a  dynamojr^mthe  earth 


178  THE    NATIONAL    ELECTRICAL    CODE. 

when  the  dynamo  and  engine  are  direct  coupled.  It  is 
therefore  considered  better  practice  (when  the  voltage 
of  the  dynamo  is  not  excessively  high)  to  depend  upon 
the  insulation  of  the  conductors  of  the  dynamo  and  not 
attempt  to  insulate  the  frame  or  body  of  the  dynamo 
from  the  earth.  If  the  frame  of  the  dynamo  is  effect- 
ively grounded,  any  defect  in  the  insulation  of  the 
dynamo  will  be  discovered  by  the  ground  detector  or 
by  an  insulation  test  made  upon  the  conductors  of  the 
system.  As  there  are  no  safety  devices  between  the 
conductors  of  a  dynamo  and  its  frame,  it  follows  that 
the  frame  should  either  be  thoroughly  insulated  or  else 
thoroughly  grounded.  Direct  coupled  machines  are 
now  the  rule  rather  than  the  exception  in  isolated 
plants,  and  the  above  rule  is  a  formal  approval  of  what 
has  been  common  practice  for  two  or  three  years. 

Rule  6,  "Lightning  Arresters,"  section  "d,"  now 
reads: 

d.  Must  be  so  constructed  as  not  to  maintain  an  arc  after  the 
discharge  has  passed,  and  must  have  no  moving  parts.  It  is  rec- 
ommended to  all  electric  light  and  power  companies  that  arrest- 
ers be  connected  at  intervals  over  systems  in  such  numbers  and  so 
located  as  to  prevent  ordinary  discharges  entering,  over  the  wires, 
buildings  connected  to  the  lines. 

The  clause  "must  have  no  moving  parts"  is  inserted 
to  shut  out  the  use  of  electro-mechanical  devices  which 
are  all  liable  to  get  out  of  order  and  nearly  all  of  which 
nave  to  be  re-set  after  one  or  after  a  few  discharges  in 
order  to  give  protection  against  the  next  discharge.  The 
placing  of  arresters  at  intervals  over  a  system  of  outside 
conductors  is  ordinary  engineering  practice.  It  is  abso- 


THE    1896    EDITION    OF    THE    CODE.  179 

lutely  essential  in  order  to  get  even  moderate  protection. 
It  has  been  clearly  shown  that  lightning  may  at  any  time 
or  place  take  a  difficult  path  to  the  earth  rather  than  travel 
a  distance  on  a  wire  to  get  to  an  easy  path.  In  practice 
this  means  that  lightning  may  go  to  the  ground  through 
a  combination  fixture  in  a  residence  rather  than  go  a 
few  hundred  feet  to  a  lightning  arrester.  The  nature  of 
the  locality  determines  where  and  how  far  apart  arrest- 
ers should  be  placed  on  any  individual  system. 

Under  Rule  8,  "  Motors,"  this  section  has  been  added: 

d.  Must  be,  when  combined  with  ceiling  fans,  hung  from  insu- 
lated hooks,  or  else  there  shall  be  an  insulator  interposed  between 
the  motor  and  its  support. 

This  rule  is  to  provide  for  the  insulation  of  motors 
used  to  run  the  horizontal  fans  now  much  used  in  res- 
taurants, etc.  It  is  evident  without  argument  that  fix- 
tures carrying  these  motors  should  be  insulated  just  as 
much  as  fixtures  carrying  incandescent  lights. 

Class  B,  High  Potential  Systems, — Under  Rule  10, 
"Outside  Conductors,"  section  "a,"  the  following 
clause  is  added: 

A  wire  with  an  insulating  covering  that  will  not  support  com- 
bustion, will  resist  abrasion,  is  at  least  ^  of  an  inch  in  thickness 
and  thoroughly  impregnated  with  a  moisture  repellant,  will  be 
approved  for  outside,  overhead  conductors,  except  service  wires. 

This  rule  simply  sanctions  what  has  for  a  long  time 
been  common  practice,  /.  ^.,  the  use  of  "weather- 
proof" wire  on  pole  lines,  with  rubber-covered  wire  for 
services  (or  wires  running  into  buildings).  Practically, 
the  only  insulation  that  can  be  expected  on  a  circuit 
run  on  poles  is  the  insulation  afforded  by  the  glass  insu- 


l8o  THE    NATIONAL    ELECTRICAL    CODE. 

lators.  Rubber  covering  on  wires  has  no  life  when 
exposed  to  the  weather,  and  in  ordinary  construction  it 
will  not  maintain  insulation  between  the  wire  and  an 
insulator.  "  The  pressure  of  the  tie  wire  and  the  swing- 
ing of  the  conductor  soon  destroy  the  insulation  of  any 
covering  at  the  insulator,  which,  as  far  as  the  conductor 
itself  is  concerned,  is  the  only  place  where  insulation  is 
needed.  The  only  advantage  of  using  anything  but  a 
bare  wire  on  a  pole  line  is  to  prevent  damage  from 
accidental  crossing  with  other  wires.  However,  con- 
sidering the  number  of  fires  that  have  been  caused  by 
such  "  crosses,"  it  appears  desirable  to  have  some  cov- 
ering for  wires.  The  first  requirement  in  this  covering 
is  durability,  and  as  "  weatherproof  "  insulation  seems 
to  be  more  durable  than  rubber  insulation  for  outdoor 
work,  and  as  weatherproof  wire  is  but  little  more  expen- 
sive than  bare  wire,  it  is  almost  universally  used  on  pole 
lines.  As  a  matter  of  fact,  there  is  not  much  insulation 
in  cotton  braid  and  black  paint.  We  should  depend 
upon  our  construction  and  not  upon  the  covering  of  the 
wire  for  insulation.  Much  weatherproof  wire  is  no 
better  than  bare  wire  except  when  perfectly  dry,  and  it 
should  always  be  treated  as  bare  wire. 

Under  Rule  12,  "All  Interior  Conductors,"  a  new 
section  has  been  added,  as  follows: 

h.  Must  be  protected  from  mechanical  injury,  when  necessary, 
on  side  walls  by  a  substantial  boxing,  retaining  an  air  space  of 
one  inch  around  the  conductors,  closed  at  the  top,  and  extending 
not  less  than  five  feet  from  the  floor.  Where  crossing  exposed 
floor  timbers  in  cellars  or  rooms,  the  conductors  must  be  attached 
by  their  insulating  supports  to  the  under  side  of  a  wooden  strip 
not  less  than  one-half  an  inch  in  thickness. 


THE    1896    EDITION    OF   THE    CODE.  l8l 

The  first  part  of  this  section  is  a  very  essential  rule. 
It  should,  of  course,  be  understood  that  the  wires  are 
led  through  the  top  of  the  boxing  and  through  the  bot- 
tom of  the  boxing,  when  the  boxing  has  a  bottom,  in 
incombustible  insulating  tubes. 

Under  Rule  13,  "Arc  Lamps,"  section  "f,"  the  fol- 
lowing is  added: 

Arc  lamps,  when  used  in  places  where  they  are  exposed  to 
flyings  of  easily  inflammable  material,  should  have  the  carbons 
enclosed  completely  in  a  globe  in  such  manner  as  to  avoid  the 
necessity  for  spark  arresters.  For  the  present,  spark  arresters 
will  not  be  required  on  so-called  "inverted  arc  "  lamps. 

Spark  arresters  were  introduced  into  use  at  a  time 
when  all  arc  lamps  were  "open"  lamps,  /'.  e.,  so  built 
that  the  top  of  the  globe  was  open.  Within  the  past 
two  or  three  years,  "enclosed  lamps,"  /.  e.,  lamps 
having  a  metal  case  enclosing  the  works  and  coming 
down  and  surrounding  the  top  of  the  globe,  have  come 
into  almost  general  use  for  inside  lighting,  and  such 
lamps  should  always  be  used  in  new  installations  in 
buildings.  The  "inverted  arc"  lamps  referred  to  are 
lamps  in  which  the  light,  instead  of  being  thrown  down- 
ward as  in  ordinary  direct  current  arc  lamps,  is  thrown 
upward  against  a  reflector,  so  that  the  lighting  is  done 
entirely  by  reflected-  light.  These  lamps  are  very  desir- 
able for  some  classes  of  lighting,  where  it  is  desirable 
to  remove  the  arc  itself  from  the  line  of  sight — though 
they  have  thus  far  been  but  little  used  in  this  country. 
The  code  allows  their  use  as  now  constructed  without 
arresters  "for  the  present,"  which  means  that  the  under- 
writers are  not  yet  ready  to  either  approve  or  condemn 


182      '  THE    NATIONAL    ELECTRICAL    CODE. 

the  existing  forms.  The  language  used  in  the  code  in 
this  connection  reminds  us  to  recommend  our  readers 
to  at  all  times  note  very  closely  the  wording  of  the 
code  in  order  to  distinguish  between  what  may,  what 
should  and  what  must  be  done. 


CHAPTER   XXI.     . 

EDITION  of  1896.     (CONCLUSION.) 

Class  C,  Low  Potential  Systems. — Under  section  18, 
"Conductors,"  Rule  "  d  "  requiring  one  foot  of  space 
between  high  and  low  potential  conductors  wherever 
they  cross  one  another,  is  omitted  and  this  rule  added: 

f.  Must  be  protected  from  mechanical  injury,  when  necessary 
on  side  walls,  by  a  substantial  boxing,  retaining  an  air  space  of 
one  inch  around  the  conductors,  closed  at  the  top,  and  extending 
not  less  than  five  feet  from  the  floor,  or  by  an  iron-armored  or  a 
metal-sheathed  insulating  conduit  sufficiently  strong  to  withstand 
the  strain  it  will  be  subjected  to,  the  inner  insulating  tubing  to  ex- 
tend one-half  inch  beyond  the  ends  of  the  metal  tube,  which  must 
extend  not  less  than  five  feet  from  the  floor.  When  crossing 
exposed  floor  timbers  in  cellars  or  rooms,  the  conductors  must  be 
attached  by  their  insulating  supports  to  the  under  side  of  a 
wooden  strip  not  less  than  one-half  inch  in  thickness  and  not  less 
than  three  inches  in  width. 

This  rule  is  the  same  one  that  has  been  added  under 
section  "b"  "High  Potential  Systems,"  except  that 
for  low  potential  circuits  armored  conduit  is  allowed  in 
place  of  boxing. 

Under  section  19,  "  Special  Rules,"  Rule  "  i "  now 
reads: 

z*.  When  from  the  nature  of  the  case  it  is  impossible  to  place 
concealed  wire  on  non-combustible  insulating  supports  of  glass  or 
porcelain,  the  wires  may  be  fished  on  the  loop  system,  if  incased 

(183) 


184  THE    NATIONAL    ELECTRICAL    CODE. 

throughout  in  approved  continuous  flexible  tubing  or  conduit. 
American  Circular  Loom  Tubing  is  approved  for  use  under  this 
rule. 

This  last  clause  is  an  addition. 

In  section  20,  '•  Mouldings/'  Rule  "  c  "  now  reads  as 
follows: 

c.  Must  be  made  of  two  pieces,  a  backing  and  capping  so  con- 
structed as  to  thoroughly  incase  the  wire  and  provide  a  one-half- 
inch  tongue  between  the  conductors,  and  a  solid  backing,  which, 
under  grooves,  shall  not  bejess  than  three-eighths  of  an  inch  in 
thickness,  and  must  afford  suitable  protection  from  abrasion.  It 
is  recommended  that  only  hardwood  moulding  be  used 

It  will  be  noted  that  three-eighths  of  an  inch  of  wood 
is  required  between  the  wires  and  the  wall  or  ceiling. 
The  preceding  edition  of  the  code  was  silent  on  this 
point,  but  the  earlier  editions  required  one-half  an 
inch,  which  made  a  rather  heavy,  clumsy  moulding. 
The  last  clause  in  Rule  "  c  "  is  an  addition. 

In  section  21,  "Special  Wiring,"  Rule  "d"  the 
following  clause  is  added: 

In  damp  places  switches  and  cut-out  blocks  must  be  mounted 
on  porcelain  knobs. 

In  section  22,  "Interior  Conduits,"  the  section  now 
opens  as  follows: 

The  American  Circular  Loom  Company  tube,  the  brass- 
sheathed  and  the  iron-armored  tubes  made  by  the  Interior  Con- 
duit and  Insulation  Company,  the  iron-armored  tube  made  by 
the  Builders'  Insulating  Company,  of  Lynn,  Mass.,  the  iron- 
armored  tube  made  by  the  Clifton  Mfg.  Co.,  of  Boston,  and  the 
Vulca  tube,  are  approved  for  the  class  of  work  called  for  in  this 
rule. 


THE    1896    EDITION    OF    THE    CODE.  185 

Rule  "e"  of  this  section  now  reads  as  follows: 

e.  Must  not  be  supplied  with  a  twin  conductor  or  two  separate 
conductors  in  a  single  tube,  except  in  an  approved  iron  or 
steel-armored  conduit.  The  use  of  approved  wires  of  oppo- 
site polarity,  either  separate  or  twin  conductor,  in  a  straight 
conduit  installation,  is  allowed  in  approved  iron-armored  or  steel- 
armored  conduits,  but  not  in  any  of  the  other  approved  conduits. 
Iron  or  steel-armored  conduit  to  be  approved  must  fulfill  the  fol- 
lowing specifications:  i.  Must  not  be  seriously  affected  externally 
by  burning  out  a  wire  inside  the  tube  when  the  iron  pipe  is  con- 
nected to  one  side  of  the  circuit.  2.  When  bent  with  a  sag  of  one 
foot  in  the  middle  of  a  ten  foot  length,  and  filled  with  water,  must 
have  an  insulation  resistance  between  the  water  and  the  iron  pipe 
of  one  megohm  after  three  days,  temperature  being  21  degrees 
Centigrade  (70  .degrees  Fahrenheit).  3.  The  insulating  material 
removed  from  the  tube  must  not  absorb  more  than  ten  per  cent, 
by  weight,  of  water  after  one  weeks'  immersion.  4.  The  insulat- 
ing material  must  not  soften  at  a  temperature  below  70  degrees 
Centigrade  (158  degrees  Fahrenheit),  and  must  leave  the  water  in 
which  it  is  boiled  practically  neutral.  5.  The  insulating  material 
must  not  become  mechanically  weak  after  three  days'  immersion 
in  water. 

All  of  this  is  very  specific  and  clear,  but  not  very 
consistent  with  a  preceding  statement  which  is  still 
retained  in  the  code  and  which  reads  as  follows: 

The  object  of  a  tube  or  conduit  is  to  facilitate  the  insertion  or 
extraction  of  the  conductors,  to  protect  them  from  mechanical 
injury,  and  as  far  as  possible,  from  moisture.  Tubes  or  conduits 
are  to  be  considered  merely  as  raceways,  and  are  not  to  be  relied 
on  for  insulation  between  wire  and  wire,  or  between  the  wire  and 
the  ground. 

In  view  of  the  new  requirements  and  the  quality  of 
the  conduits  now  on  the  market,  it  will  be  interesting  to 
watch  for  reports  of  the  Underwriters'  Electrical 


l86  THE    NATIONAL    ELECTRICAL    CODE. 

Bureau,  to  see  what  makes  of  iron  conduits  are  approved^ 
The  practice  of  running  two  wires  in  one  iron  tube  is 
the  best  in  most  cases  and  is  the  only  allowable  method 
in  many  cases — as  for  example  when  alternating  cur- 
rents are  used  and  in  modern  steel  construction  fire- 
proof buildings.  We  believe,  however,  that  the  high 
standard  of  insulation  required  for  the  lining  of  a  tube 
is  out  of  all  reason;  since  there  is  no  method  for  mak- 
ing such  insulation  at  joints.  In  view  of  the  fact  that 
the  question  of  using  any  lining  at  all,  except  to  prevent 
rust,  is  still  under  discussion,  we  believe  that  the  con- 
duit should,  for  the  present  at  least,  be  considered  as  a 
hole  and  nothing  else.  Such  a  treatment  ought  to 
develop  the  manufacture  of  good  insulated  wire  and 
will  not  prevent  anyone  from  putting  another  insulation 
around  his  wire  if  he  sees  fit.  We  do  not  think  an  insu- 
lating lining  will  injure  a  conduit,  and,  for  that  matter, 
it  would  do  no  harm  to  run  the  conduit  on  porcelain 
insulators,  but  we  think  the  code  should  be  consistent, 
and  there  is  a  conduit  now  on  the  market  which  is  all 
right  if  people  will  only  pay  for  it  and  use  it. 

In  section  23,  ''Double  Pole  Cut-outs,"  Rule  "f," 
which  requires  that  the  cut-out  block  be  stamped  with 
the  maximum  safe  carrying  capacity,  is  omitted. 

In  section  27,  "Fixture  Work,"  under  Rule  "  a,"  it  is 
required  that  insulating  joints  be  placed  as  close  as 
possible  to  the  ceiling  and  the  following  is  added: 

It  is  recommended  that  the  gas-outlet  pipe  be  protected  above 
the  insulating  joint  by  a  non-combustible,  non-absorptive,  insu- 
lating tube  having  a  flange  at  the  lower  end,  where  it  comes  in 
contact  with  the  insulating  joint,  and  that  where  outlet  tubes  are 
used,  they  be  of  sufficient  length  to  extend  below  the  joint,  and 


THE    1896    EDITION    OF    THE    CODE.  187 

that  they  be  so  secured  that  they  will  not  be  pushed  back  when 
the  canopy  is  put  in  place..  Where  iron  ceilings  are  used,  care 
must  be  taken  to  see  that  the  canopy  is  thoroughly  and  perma- 
nently insulated  from  the  ceiling. 

Those  of  our  readers  who  are  familiar  with  wiring 
and  with  combination  fixtures  and  insulating  joints  will 
appreciate  the  object  of  this  rule  and  the  need  of  some 
such  regulations.  Those  who  are  not  familiar  with  the 
details  of  construction  will  hardly  get  a  clear  idea  of 
what  is  intended  from  reading  the  rule  or  from  this 
brief  statement  However,  all  will  appreciate  the  fact 
that  one  of  the  greatest  danger  points  in  any  system  is 
where  gas  and  electricity,  wires  and  a  grounded  pipe, 
wiremen  and  gas  fitters  all  come  together.  The  rule  is 
intended  to  accomplish  the  following  essential  things: 
First,  to  keep  the  pipe  of  the  fixture  insulated  from  the 
grounded  gas  pipes;  second,  to  keep  the  wires  leading 
to  the  fixture  away  from  the  grounded  gas  pipe;  third, 
to  keep  the  insulated  fixture  from  coming  into  contact 
with  a  grounded  gas  pipe  or  grounded  ceiling,  through 
the  ornamental  canopy  which  is  used  as  a  trim  and  to 
hide  the  joints  in  the  pipe  and  wires. 

In  section  28,  "Arc  Lights  on  Low  Potential  Cir- 
cuits," Rule  "a,"  requiring  No.  12  B.  &  S.  wire  for 
branch  conductors,  is  omitted,  the  size  of  the  wire 
being  left  to  the  table  of  "carrying  capacities."  If 
proper  fuses  are  used  to  protect  the  wires,  no  such  rule 
is  needed.  Still,  it  was  a  pretty  good  rule  not  to  use  a 
wire  smaller  than  No.  12  B.  &  S.  for  a  pair  of  low  am- 
pere lamps  connected  in  series.  Most  lamps  now  on 
the  market  take  an  abnormal  current  on  starting;  and 
the  defective  operation  of  one  lamp  tends  to  increase 


l88  THE    NATIONAL    ELECTRICAL    CODE. 

the  current  in  the  circuit,  so  that  it  is  good  practice  to 
put  in  a  wire  in  a  tap  circuit  of  this  kind  which  is  large 
enough  to  carry  about  twice  the  normal  current  of  the 
lamp. 

In  section  31,  "Flexible  Cord,"  Rule  "a"  is  revised 
to  read: 

31.  FLEXIBLE  CORD:—  a.   Must  be  made  of  two-stranded  con- 
ductors, each   having  a  carrying  capacity  equivalent   to  not  less 
than   a  No.  16  B.  &  S    wire,  and  each  covered   by  an  approi'ed 
insulation,  and  protected  by  a  slow-burning,  tough,  braided  outer 
covering.    Insulation  for  pendants  under  this  rule  must  be  moist- 
ure and  flame-proof.     Insulation  ion  fixture  work  must  be  water- 
proof, durable  and  not  easily  abraided.    Insulation  for  cords  used 
for  all  other  purposes,  including  portable  lamps  and  motors,  must 
be  solid,  at  least  ^  of  an  inch  in  thickness,  and  must  show  an 
insulation  resistance  between  conductors  and  between  either  con- 
ductor and  the  ground  of  at  least  one  megohm  per  mile,  after  one 
week's  immersion  in  water  at  70  degrees  Fahrenheit,  with  a  cur- 
rent of  550  volts,  and  after  three  minutes'  electrification. 

This  requires  that  a  flexible  cord  shall  have  an  insu- 
lation which  is  practically  as  good  as  that  of  any  other 
conductor.  This  is  only  reasonable  as,  of  all  parts  of 
a  circuit,  flexible  cords  are  subjected  to  the  worst  con- 
ditions and  treatment,  and  they  are  often  located  in 
places  where  a  little  flash  would  cause  a  fire.  The  cord 
question  is  still  a  problem,  and  it  is  well  to  know  what 
kind  and  what  makes  of  cord  the  underwriters  approve. 

Section  32,  "  Decorative  Lamps,"  is  changed  to 
read  : 

32.  DECORATIVE  SERIES  LAMPS: —Incandescent  lamps  run  in 
series  circuits  shall  not  be  used  for  decorative  purposes   inside   of 
buildings,  except  by  special  permission  in  writing  from  the  under- 
writers having  jurisdiction. 


THE     1896    EDITION    OF    THE    CODE.  189 

This  change  seems  only  fair,  as  the  only  commercial 
"  decorative  "  lamps  have  to  be  run  in  series  on  ordi- 
nary circuits,  and  there  are  many  places  where  they  are 
wanted  and  where  they  can  be  used  with  safety. 

Class  D,  Alternating  System. — Section  34,  now 
reads  : 

34.    IN    THOSE    CASES    WHERE    IT    MAY    NOT    BE    POSSIBLE    TO    Ex- 

CLUDE  THE  CONVERTERS  AND  PRIMARY  WlRES  ENTIRELY  FROM  THE 
BUILDING,  THE  FOLLOWING  PRECAUTIONS  MUST  BE  STRICTLY 
OBSERVED: — Converters  must  be  located  at  a  point  as  near  as  pos- 
sible to  that  at  which  the  primary  wires  enter  the  building,  and 
must  be  placed  in  an  inclosure  constructed  of  or  lined  with  fire- 
resisting  material;  the  inclosure  to  be  used  only  for  this  purpose, 
and  to  be  kept  securely  locked,  and  access  to  the  same  allowed 
only  to  responsible  persons.  They  must  be  effectually  insulated 
from  the  ground  and  the  enclosure  in  which  they  are  placed  must 
be  practically  air-tight,  except  that  it  shall  be  thoroughly  venti- 
lated to  the  out-door  air,  if  possible,  through  a  chimney  or  flue. 
There  should  be  at  least  six  inches  air  space  on  all  sides  of  the 
converter. 

This  section  might  be  changed  again  without  hurting 
it.  The  building  of  a  thoroughly  ventilated  and  yet 
air-tight  room  is  a  problem  that  is  a  little  out  of  the 
ordinary  for  an  every  day  electrical  constructor.  It 
might  be  made  air  tight,  too,  as  regards  the  building, 
and  ventilated  into  the  outer  air  by  using  two  flues  and 
a  ventilating  fan  to  create  a  draft,  but  plans  should 
accompany  such  a  specification  as  the  one  in  the  code. 
Again,  it  is  considered  by  many  experienced  men  that 
the  grounding  of  transformer  cases  in  basements,  'is 
good  practice.  Any  one  standing  on  a  basement  floor 
is  pretty  sure  to  be  electrically  connected  to  the  earth 
and  the  converter  case  had  better  be  in  the  same  con- 


IQO  THE    NATIONAL    ELECTRICAL    CODE. 

dition,  unless  it  is  in  a  converter  room  which  is  always 
kept  locked  and  the  key  in  the  possession  of  an  experi- 
enced and  careful  man.  Otherwise  there  is  liable  to  be 
a  loss  to  a  life  insurance  company.  The  rule  is  all 
right  in  one  point,  /'.  e.t  it  recognizes  the  fact  that  any 
restrictions  are  justified  that  may  be  necessary  to  secure 
safety.  When  converters  are  placed  in  buildings  they 
should  be  made  safe  regardless  of  expense.  The  only 
question  is  as  to  the  surest  way  of  doing  it. 

Class  E,  Electrical  Railways. — This  part  of  the 
code  is  unchanged  except  in  section  42,  "Car  Houses." 
This  section  now  reads  as  follows: 

42.  CAR  HOUSES: — a.  Must  have  the  trolley  wires  properly 
supported  on  insulating  hangers,  b.  Must  have  the  trolley  hang- 
ers placed  at  such  a  distance  apart  that  in  case  of  a  break  in  the 
trolley  wire,  contact  cannot  be  made  with  the  floor,  c.  Must 
have  cut-out  switch  located  at  a  proper  place  outside  the  building, 
so  that  all  trolley  circuits  in  the  building  can  be  cut  out  at  one 
point,  and  the  line  circuit  breakers  must  be  installed,  so  that  when 
this  cut-out  switch  is  open  the  trolley  wire  will  be  dead  at  all 
points  within  100  feet  of  the  building.  The  current  must  be  cut 
out  of  the  building  whenever  the  same  is  not  in  use,  or  the  road 
not  in  operation,  d.  Must  have  all  lamps  and  stationary  motors 
installed  in  such  a  way  that  one  main  switch  can  control  the 
whole  of  each  installation  (lighting  or  power),  independently  of 
main  feeder  switch.  No  portable  incandescent  lamps  or  twin 
wire  allowed,  except  that  portable  incandescent  lamps  may 
be  used  in  the  pits;  connections  to  be  made  by  two  approved 
rubber-covered  flexible  wires,  properly  protected  against  mechan- 
ical injury;  the  circuit  to  be  controlled  by  a  switch  placed  outside 
the  pit.  e.  Must  have  all  wiring  and  apparatus  installed  in 
accordance  with  rules  under  Class  B.  f.  Must  not  have  any  sys- 
tem of  feeder  distribution  centering  in  the  building,  g:  Must 
have  the  rails  bonded  at  each  joint  with  not  less  than  No.  2  B  & 


THE    1896    EDITION    OF    THE    CODE.  191 

S.  annealed  copper  wire;  also  a  supplementary  wire  to  be  run  for 
each  track,  h.  Must  not  have  cars  left  with  trolley  in  electrical 
connection  with  the  trolley  wire. 

The  use  of  a  street  railway  current  of  500  volts  pres- 
sure is  not  allowed  in  any  building  except  street  railway 
power  houses  and  car  barns,  and  in  these  last  it  is 
practically  a  necessity.  The  code  permits  such  usage, 
but- requires  almost  every  precaution  that  can  be  sug- 
gested. Rule  "e"  requires  that  the  wires  be  run  in 
the  same  manner  as  for  high  potential  systems.  Rule 
"f"  prohibits  the  placing  of  conductors  in  the  car 
barn  for  any  purpose  except  the  necessary  service  of  the 
barn.  Rule  "a"  requires  the  use  of  the  same  insula- 
tion that  is  used  on  the  trolley  wires  out  of  doors. 
Rule  "b"  is  to  prevent  the  possibility  of  a  flash  in 
case  the  trolley  wire  should  break  and  come  into  contact 
with  the  rails,  which  are  electrically  connected  to  the 
track  outside  the  barn,  as  per  Rule  "g,"  and  therefore 
of  opposite  polarity.  Rule  ''h"  prevents  the  possi- 
bility of  the  cars  taking  fire  in  the  car  barris.  Rules 
"c"  and  "d"  insist  on  such  an  installation  that  any 
circuit  not  in  proper  condition  or  not  needed  can  be 
instantly  disconnected,  and  that  when  electricity  is  not 
needed  in  the  barn,  no  current  can  pass  into  it  from  the 
trolley  wires  or  feeders.  This  last  requirement  is  very 
essential  to  protect  the  barn  against  lightning.  For 
those  who  are  not  familiar  with  car  barns  we  will  say 
that  the  "pits"  referred  to  are  located  between  the 
rails  of  each  track  inside  the  barn  so  that  a  man  can 
get  into  a  "pit,"  and  thus  have  room  under  a  car  to 
examine  and  repair  the  motors  and  running  gear. 


IQ2  THE    NATIONAL    ELECTRICAL    CODE. 

Naturally  a  man  wants  a  light  for  such  work,  and  if  he 
cannot  have  an  incandescent  light  he  will  take  a  torch. 
In  spite  of  the  apparent  difficulty  in  securing  safety  in 
car  barns,  the  use  of  electricity,  with  such  construc- 
tion as  is  required  by  the  above  rule,  is  quite  safe,  and 
infinitely  safer  than  lighting  the  barn  with  gas,  "oil, 
torches,  etc.  The  fact  that  the  lights,  motors,  etc., 
are  used  only  by  men  who  know  how  electricity  acts  at 
500  volts  pressure  on  a  grounded  circuit,  reduces  the 
danger  to  life  and  property  to  a  minimum,  but  the  use 
of  such  a  current  in  a  car  barn  should  not  be  taken  as 
an  argument  for  allowing  its  use  promiscuously. 

Class  F,  Electrical  Heaters. — This  is  the  heading  of 
a  new  class  in  the  revised  code;  the  text  is  as  follows: 

44.  CLASS  F.  ELECTRICAL  HEATER: — a.  If  stationary,  must  be 
placed  in  a  safe  situation,  isolated  from  inflammable  materials 
and  treated  as  stoves.  b.  Must  have  double-pole  indicating 
switches  and  double-pole  cut-outs  arranged  as  required  for  elec- 
tric light  or  power  of  same  potential  and  current,  c.  Must  have 
the  attachments  of  feed  wires  to  the  heaters  in  plain  sight,  easily 
accessible  and  protected  from  interference,  accidental  or  other- 
wise, d.  The  flexible  conductors  for  portable  apparatus,  such  as 
irons,  etc.,  must  have  an  insulation  that  will  not  be  injured  by 
heat,  such  as  asbestos,  which  must  be  protected  from  mechanical 
injury  by  an  outer  substantial  braided  covering,  and  so  arranged 
that  mechanical  strain  will  not  be  borne  by  the  electrical  connec- 
tions. 

Sections  "a,"  "b"  and  "c"  are  self-explanatory. 
Section  "d"  is  necessitated  by  the  fact  that  the  appli- 
ances mentioned  are  used  in  a  careless  manner,  being 
operated  for  the  most  part  by  people  who  do  not 
appreciate  the  damage  that  may  be  caused  by  improper 
usage. 


THE    1896    EDITION    OF    THE    CODE.  193 

Miscellaneous. — In  Rule  46,  section  "a"  every  cir- 
cuit is  required  to  have  an  insulation  of  at  least 
100,000  ohms  instead  of  25,000  ohms,  as  in  the 
preceding  edition.  This  standard  is  surely  low  enough, 
and  to  make  it  any  lower  is  absurd,  when  4,000,000 
ohms  is  required  for  an  installation  of  10  amperes, 
which  is  a  greater  current  than  is  carried  by  the 
ordinary  branch  circuit.  Two  circuits  with  an  insu- 
lation resistance  of  100,000  ohms  each  would  bring  the 
insulation  of  an  8oo-light  plant  way  below  the  80,000 
ohms  required.  In  most  plants  an  insulation  resist- 
ance of  a  megohm  (1,000,000)  ohms  per  circuit  is  low 
enough  to  allow,  but  as  a  universal  rule  the  100,000 
ohm  limit  is  all  right  when  taken  in  connection  with 
the  table  which  follows  in  the  code. 

Section  "e"  of  the  old  code  is  made  section  "f  "in 
the  revised  code,  and  the  following  section  is  added: 

e.  The  metallic  sheathes  to  cables  must  be  permanently  and 
effectually  connected  to  earth. 

The  utility  of  this  rule  in  all  cases  may  be  ques- 
tioned, but  it  is  probably  based  upon  results  obtained 
in  practice.  These  miscellaneous  rules  will  probably 
be  revised  many  times;  but  as  they  now  stand  they  are 
far  ahead  of  practice.  '  At  the  present  time  each  man 
protects  his  particular  system  of  conductors  as  best  he 
can.  The  leading  electric  light  companies  are  in 
advance  of  the  code  in  their  practice,  and  the  ordinary 
small  unmanaged  company  has  its  system  protected  by 
guesswork  and  Providence. 

Wires, — The  code  of  January  ist,  1896,  publishes  a 
new  list  of  wires,  as  follows1 

13 


194  THE    NATIONAL    ELECTRICAL    CODE. 

WIRES: — The  following  is  a  list  of  wires  which  have  been 
tested  and  been  found  to  comply  with  the  standard  for  approved 
wires,  required  for  all  high  potential  work  (300  volts  or  over)  and 
for  service  wires,  all  classes  of  concealed  wiring  and  wiring 
exposed  to  dampness  in  low  potential  work: — 

Name  of  Wire.  Manufacturer. 

Americanite American  Electrical  Works. 

Bishop , Bishop  Gutta  Percha  Co. 

Clark Eastern  Electric  Cable  Co. 

Climax Simplex- Electric  Co. 

Simplex  (caoutchouc) Simplex  Electric  Co. 

Crescent   John  A.  Roebling's  Sons  Co. 

Crown Washburn  &  Moen. 

Globe Washburn  &  Moen. 

Salamander Washburn  &  Moen. 

Crefeld Crefeld  Electrical  Works. 

Grimshaw  (White  core) N.  Y.  Insulated  Wire  Co. 

Raven  core N.  Y.  Insulated  Wire  Co. 

Requa  (White  core) Safety  Insulated  Wire  &  Cable  Co. 

Safety  (Black  core) Safety  Insulated  Wire  &  Cable  Co. 

Habirshaw  (White  core) Ind.  Rubber  &  Gutta  Percha  Ins.  Co. 

Habirshaw  (Blue  core) Ind.  Rubber  &  Gutta  Percha  Ins.  Co. 

Habirshaw  (Red  core) Ind.  Rubber  &  Gutta  Percha  Ins.  Co. 

Paranite  Indiana  Rubber  &  Insulated  Wire  Co 

Liberty Atlas  Covering  Works. 

Kerite    W.  R.  Brixey. 

Okonite Okonite  Co. 

Paracore Nat.  India  Rubber  Co. 

N.  I.  R Nat.  India  Rubber  Co. 

U.  S General  Electric  Co. 

Columbia C.  S.  Knowles. 

NOTE. — The  results  of  recent  tests  on  these  and  other  wires 
can  be  seen  at  inspection  office. 

Whatever  we  had  to  say  about  the  old  list  applies  to 
this  list  as  well.  Rubber  covered  wire  has  steadily 


THE    1896    EDITION    OF    THE    CODE.  195 

become  cheaper ;  we  hope  it  has  at  the  same  time 
become  better,  but  we  fear  it  has  not.  One  thing  is 
certain,  for  high  potentials  and  damp  places  the  best 
is  none  too  good  and  the  best  is  certainly  the  cheapest. 
Any  portion  of  the  code  to  which  we  have  not 
referred  in  this  and  the  next  preceding  chapter  remains 
unchanged.  In  this  book  we  have  tried  to  explain  the 
meaning  and  object  of  the  code,  and  we  will  close  with 
a  brief  statement  concerning  its  limitation.  The  object 
of  the  code  is  to  secure  safety,  nothing  else.  It  does 
not  indicate  how  to  install  a  plant  so  as  to  get  reliable 
service,  or  even  and  uniform  lighting.  The  code 
insists  upon  the  use  of  the  best  methods  and  materials 
that  can  be  insisted  upon  without  making  the  use  of 
electricity  prohibitive  or  working  a  hardship  upon  the 
user.  The  code  is  not  a  specification  of  how  to  install 
an  electric  plant,  and  it  should  not  be  used  as  a  substi- 
tute for  one.  It  simply  tells  what  must,  and  what  must 
not  be  done,  in  order  to  secure  safety.  When  care- 
fully studied,  it  indicates  the  methods  and  means  to  be 
adopted  to  secure  safety  in  all  cases.  As  the  art  ad- 
vances, the  application  of  electricity  will  become  more 
safe  and  the  requirements  of  the  code  will  become  more 
rigid.  It  is  susceptible  of  many  improvements,  but  as 
it  exists  today,  it  is  far,  far  ahead  of  general  practice. 
Only  in  a  few  large  cities  is  the  standard  of  the  code 
even  approximately  maintained;  and  it  should  be  the 
aim  of  every  electrical  engineer  and  every  man  inter- 
ested in  fire  insurance  to  try  to  raise  the  practice  to  the 
standard  of  the  code.  Although  we  have  taken  up  more 
space  than  we  originally  anticipated,  we  feel  that,  so 


t(j6  THE    NATIONAL    ELECTRICAL    CODE. 

far  from  exhausting  the  subject,  we  have  only  been 
able  to  cover  it  in  a  very  superficial  manner;  but  we 
trust  that  we  have  at  least  shown  that  the  code  is 
worthy  of  careful  study  by  every  one  interested  in  the 
application  of  electricity,  and  hope  we  have  aided  our 
readers  in  obtaining  an  understanding  of  its  principles. 


APPENDIX. 


TABLES   AND   CURVES. 

The  accompanying  table  and  curves  show  the  relations  exist- 
ing between  the  sectional  area  and  the  "maximum  safe  carrying 
capacity  "  of  insulated  copper  wires. 

Explanation  of  Table. — Columns  I.,  IV.  and  VI.  are  the  same 
as  given  in  the  Code.  Column  II.  gives  the  diameter  of  the  wires 
in  inches,  and  column  III.  gives  the  corresponding  circular  mils. 
In  ordinary  computations  and  comparisons,  circular  mils  are 
used  instead  of  areas.  The  circular  mils  of  a  wire  are  propor- 
tional to  its  sectional  area.  The  square  mils  may  be  obtained 
from  the  circular  mils  by  multiplying  by  .7854,  and  the  sectional 
area  in  square  inches  may  be  obtained  by  dividing  the  square 
mils  by  1,000,000.  Column  V.  is  obtained  by  division  from  col- 
umns III.  and  IV.;  and  column  VII.  is  obtained  in  the  same  way 
from  columns  III.  and  VI. 

Explanation  of  Curves: — Curves  IV.,  V.,  VI.  and  VII.  repre- 
sent graphically  the  columns  correspondingly  numbered  in  the 
table.  To  find  the  carrying  capacity  of  any  -wire  from  the 
curves. — On  the  base  line  marked  circular  mils,  find  the  point 
corresponding  to  the  circular  mils  of  the  wire.  Follow  up  the 
vertical  line  through  this  point  until  it  intersects  curve  IV.  or  VI., 
according  as  the  wire  is  to  be  concealed  or  open.  From  this 
intersection  point  follow  horizontal  line  to  the  vertical  line  marked 
"Amperes."  The  desired  number  in  amperes  can  then  be  read 
on  this  vertical  line.  To  find  the  corresponding  circular  mils  per 
ampere,  follow  the  same  method  with  curves  V.  or  VII. 

(197) 


TABLE  SHOWING  RELATION  BETWEEN  SIZE  AND  SAFE  CARRYING 
CAPACITY  OF  INSULATED  COPPER  WIRES. 


CONCEALED  WORK. 

OPEN  WORK. 

Diam- 

Sectional 

Size 

eter  of 

Area  in 

B.  &S. 

Wire  in 

Circular 

Safe  Carry- 

Circular 

Safe  Carry- 

Circular 

Gauge. 

Inches. 

Mils. 

ing  Capa- 

Mils 

ing  Capa- 

Mils 

city  in 

per  Am- 

city  in 

per  Am 

Amperes.    ;        pere. 

Amperes. 

pere. 

I~ 

II. 

III. 

IV. 

V. 

VI. 

VII. 

0000 

.46 

2II6OO 

218 

97! 

312 

679 

000 

.4096 

167800  ' 

181 

927 

262 

640 

00 

.3648 

I33IOO 

150 

887 

22O 

605 

"0 

•325 

105500 

125 

844 

I85 

570 

I 

3893 

83600 

105 

797 

I56 

536 

2 

.2576 

66370 

88 

754 

131 

507 

3 

.2294 

52630 

75 

702 

no 

478 

4 

.2043 

41740 

63 

662 

92 

453 

5 

.1819 

33100 

53 

625 

77 

430 

6 

.1620 

26250 

45 

583 

65 

404 

8 

.1285 

16510 

33 

500 

46 

359 

10 

.1019 

10380 

25 

4i5 

32 

325 

12 

.0808 

6530 

17 

384 

23 

283 

14 

.0641 

4107 

12 

342 

16 

257 

16 

.0508 

2583 

6 

43i 

8 

323 

18 

.0403 

1624 

3 

541 

5 

325 

NOTE. — The  "  circular  mils  "  of  a  wire  is  the  square  of  the 
diameter  expressed  in  thousandths  of  an  inch. 

If  D  =  diameter  of  wire  in  inches  (column  II.),  then  circular 
mils  =  D2  X  1,000,000  (column  III.). 


(198) 


(2) 


APPENDIX. 


RULES  AND  REQUIREMENTS 

OF   THE 

NATIONAL  BOARD  OF  FIRE  UNDERWRITERS 

For  the  Installation  of  Wiring  and  Apparatus  for  Electric  Light, 
Heat  and  Power  as  Recommended  by  the  Underwriters' 
National  Electric  Association. 

Edition  of  January  i,  1896. 
GENERAL  SUGGESTIONS. 

In  all  electric  work  conductors,  however  well  insulated,  should 
always  be  treated  as  bare,  to  the  end  that  under  no  conditions, 
existing  or  likely  to  exist,  can  a  grounding  or  short  circuit  occur, 
and  so  that  all  leakage  from  conductor  to  conductor,  or  between 
conductor  and  ground,  may  be  reduced  to  the  minimum. 

In  all  wiring  special  attention  must  be  paid  to  the  mechanical 
execution  of  the  work.  Careful  and  neat  running,  connecting, 
soldering,  taping  of  conductors  and  securing  and  attaching  of 
fittings,  are  specially  conducive  to  security  and  efficiency,  and 
will  be  strongly  insisted  on. 

In  laying  out  an  installation  the  work  should,  if  possible,  be 
started  from  a  center  of  distribution,  and  the  switches  and  cut- 
outs, controlling  and  connected  with  the  several  branches,  be 
grouped  together  in  a  safe  and  easily  accessible  place,  where  they 
can  be  readily  got  at  for  attention  or  repairs.  The  load  should  be 
divided  as  evenly  as  possible  among  the  branches  and  all  compli- 
cated and  unnecessary  wiring  avoided. 

The  use  of  wire-ways  for  rendering  concealed  wiring  perma- 
nently accessible  is  most  heartily  endorsed  and  recommended; 

(201) 


2O2       RULES  AND  REQUIREMENTS  OF  THE 

and  this  method  of  accessible  concealed  construction  is  advised  for 
general  use. 

Architects  are  urged,  when  drawing  plans  and  specifications, 
to  make  provision  for  the  channeling  and  pocketing  of  buildings 
for  electric  light  or  power  wires,  and  in  specifications  for  electric 
gas  lighting  to  require  a  two-wire  circuit,  whether  the  building  is 
to  be  wired  for  electric  lighting  or  not,  so  that  no  part  of  the  gas 
fixtures  or  gas  piping  be  allowed  to  be  used  for  the  gas-lighting 
circuit. 

CLASS  A,  CENTRAL  STATIONS. 

FOR    LIGHT    OR    POWER 

(These  rules  also  apply  to  dynamo  rooms  in  isolated  plants  con- 
nected with  or  detached  from  buildings  used  for  other  purposes; 
also  to  all  varieties  of  apparatus  therein  of  both  high  and  low 
potential). 

1.  GENERATORS: — 

a.  Must  be  located  in  a  dry  place. 

b.  Must  be  insulated  on  floors  or  base  frames,  which  must  be 
kept  filled  to  prevent  absorption  of  moisture,  and  also  kept  clean 
and  dry.     Where  frame  insulation  is  impossible,  the  Inspector 
may,  in  writing,  permit  its  omission,  in  which  case  the  frame  must 
be  permanently  and  effectively  grounded. 

c.  Must  never  be  placed  in  a  room  where  any  hazardous  pro- 
cess is  carried  on,  nor  in  places  where  they  would  be  exposed  to 
inflammable  gases  or  flyings  of  combustible  material. 

d.  Must  each  be  provided  with  a  waterproof  covering. 

2.  CARE  AND  ATTENDANCE:— 

A  competent  man  must  be  kept  on  duty  in  the  room  where 
generators  are  operating. 

Oily  waste  must  be  kept  in  approved  metal  cans  and  removed 
daily. 

Approved  waste  cans  shall  be  made  of  metal,  with  legs  raising  can  three 
inches  from  the  floor,  and  with  self-closing  covers. 

3.  CONDUCTORS: — 

From  generators,  switchboards,  rheostats  or  other  instruments, 
and  thence  to  outside  lines,  conductors 

a.  Must  be  in  plain  sight  or  readily  accessible. 

b.  Must  be  wholly  on  non-combustible  insulators,  such  as  glass 
or  porcelain. 

c.  Must  be  separated  from  contact  with  floors,   partitions  or 
walls,  through  which  they  may  pass,  by  non-combustible  insulat- 
ing tubes,  such  as  glass  or  porcelain. 


UNIVERSITY 

NATIONAL    BOARD    OF    FIRE    U&DRKWSi££RS 


d.  Must  be  kept  rigidly  so  far  spart  that  they  cannot  come  in 
contact 

<?.  Must  be  covered  with  non-inflammable  insulating  material 
sufficient  to  prevent  accidental  contact,  except  that  "bus  bars  ' 
may  be  made  of  bare  metal, 

f.  Must  have  ample  carrying  capacity  to  prevent  heating.  (See 
Table  of  Capacity  of  Wires.) 

4      SWITCHBOARDS:  — 

a.  Must  be  so  placed  as  to  reduce  to  a  minimum  the  danger  of 
communicating  fire  to  adjacent  combustible  material 

Special  attention  is  called  to  the  fact  that  switchboards  should  not  be  built 
down  to  the  floor,  nor  up  to  the  ceiling,  but  a  space  of  at  least  eighteen  inches,  or 
two  feet,  should  be  left  between  the  floor  and  the  board,  and  between  the  ceiling 
and  the  board,  in  order  to  prevent  fire  from  communicating  from  the  switchboard 
to  the  floor  or  ceiling,  and  also  to  prevent  the  forming  of  a  partially  concealed 
space  very  liable  to  be  used  for  storage  or  rubbish  and  oily  waste. 

b.  Must  be  accessible  from  all  sides  when  the  connections  are 
on  the  back;  or  may  be  placed  against  a  brick  or  stone  wall  when 
the  wiring  is  entirely  on  the  face. 

c.  Must  be  kept  free  from  moisture. 

d.  Must  be  made  of  non-combustible  material,  or  of  hardwood 
in  skeleton  form,  filled  to  prevent  absorption  of  moisture. 

e.  Bus  bars  must  be  equipped  in  accordance  with  Rule  3  for 
placing  conductors. 

5.  RESISTANCE  BOXES  AND  EQUALIZERS:  — 

a.  Must  be  equipped  with  metal,  or  other  non-combustible 
frames. 

The  word  "frame"  in  this  section  relates  to  the  entire  case  and  surroundings 
of  the  rheostat,  and  not  alone  to  the  upholding  supports. 

b.  Must  be  placed  on  the  switchboard,  or,  if  not  thereon,  at  a 
distance  of  a  foot  from  combustible  material,  or  separated  there- 
from by  a  non-inflammable,  non-absorptive,  insulating  material. 

6.  LIGHTNING  ARRESTERS:  — 

a.  Must  be  attached  to  each  side  of  every  overhead  circuit 
connected  with  the  station. 

b.  Must  be  mounted  on  non-combustible  bases  in  plain  sight 
on  the  switchboard,  or  in  any  equally  accessible  place,  away  from 
combustible  material. 

c.  Must  be  connected  with  at  least  two  "  earths  "  by  separate 
metallic  strips  or  wires  having  a  conductivity  not  less  than  that  of 
a  No.  6  B.  &  S.  wire.    These  strips  or  wires  must  be  run  as  nearly 
as  possible  in  a  straight  line  from  the  arresters  to  the  earth  con- 
nection. 


2O4       RULES  AND  REQUIREMENTS  OF  THE 

d.  Must  be  so  constructed  as  not  to  maintain  an  arc  after  the 
discharge  has  passed,  and  must  have  no  moving  parts. 

It  is  recommended  to  all  electric  light  and  power  companies  that  arresters  be 
connected  at  intervals  ever  systems  in  such  numbers  and  so  located  as  to  prevent 
ordinary  discharges  entering,  over  the  wires,  buildings  connected  to  the  lines. 

7.  TESTING: — 

a.  All  series  and  alternating  circuits  must  be  tested  every  two 
hours  while  in  operation  to  discover  any  leakage  to  earth,  abnor- 
mal in  view  of  the  potential  and  method  of  operation. 

b.  All  multiple  arc  low-potential   systems  (300  volts  or  less) 
must  be  provided  with  an  indicating  or  detecting  device,  readily 
attachable,  to  afford  easy  means  of  testing. 

c.  Data  obtained  from  all  tests  must  be  preserved  for  examina- 
tion by  insurance  inspectors. 

These  rules  on  testing  to  be  applied  at  such  places  as  may  be 
designated  by  the  association  having  jurisdiction. 

8.  MOTORS: — 

a.  Must  be  wired  under  the  same  precautions  as  with  a  cur- 
rent of  the  same  volume  and  potential  for  lighting.     The  motor 
and  resistance  box  must  be  protected  by  a  double-pole  cut-out 
and  controlled  by  a  double-pole  switch,  said  switch  plainly  indi- 
cating whether  "  on  "  or  "off,"  except  in  cases  where  one-quarter 
horse-power  or  less  is  used  on  low-tension  circuits  a  single-pole 
switch  will  be  accepted. 

b.  Must  be  thoroughly  insulated,  mounted  on  filled,  dry  wood, 
be  raised  at  least  eight  inches  above  the  surrounding  floor,  be 
provided  with  pans  to  prevent  oil  from  soaking  into  the  floor,  and 
must  be  kept  clean. 

c.  Must  be  covered  with  a  waterproof  cover  when  not  in  use. 
and,   if  deemed  necessary  by  the  inspector,  be  inclosed  in  an 
approved  case. 

From  the  nature  of  the  question,  the  decision  as  to  what  is  an  approved  case 
must  be  left  to  the  inspector  to  determine  in  each  instance. 

d.  Must  be,  when  combined  with  ceiling  fans,  hung  from  insu- 
lated hooks,  or  else  there  shall  be  an  insulator  interposed  between 
the  motor  and  its  support. 

9.  RESISTANCE  BOXES: — 

a.  Must  be  equipped  with  metal  or  other  non-combustible 
frames. 

The  word  "  frame"  in  this  section  relates  to  the  entire  case  and  surroundings 
of  the  rheostat,  and  not  alone  to  the  upholding  supports. 

b.  Must  be  placed  on  the  switchboard,  or  at  a  distance  of  a 
foot  from  combustible  material,  or  separated  therefrom  by  a  non- 
inflammable,  non-absorptive  insulating  material. 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.          20$ 

CLASS  B,   HIGH  POTENTIAL  SYSTEMS 
(OVER  300  VOLTS  ) 

(Any  circuit  attached  to  any  machine,  or  combination  of  ma 
chines,  which  develops  over  300  volts  difference  of  potential 
between  any  two  wires,  shall  be  considered  as  a  high  potential 
circuit  and  coming  under  that  class,  unless  an  approved  trans- 
forming device  is  used  which  cuts  the  difference  of  potential  down 
to  less  than  300  volts.) 

10.  OUTSIDE  CONDUCTORS: — 

All  outside,  overhead  conductors  (including  services) 

a.  Must  have  an  approved  insulating  covering,  and  be  firmly 
secured  to  properly  insulated  and  substantially  built  supports,  all 
tie   wires  having  an  insulation  equal  to  that  of  the  conductors 
they  confine. 

Insulation  that  will  be  approved  for  service  wires  must  be  solid,  at  least  A  of 
an  inch  in  thickness  and  covered  with  a  substantial  braid.  It  must  not  readily 
carry  fire,  must  show  an  insulating  resistance  of  one  megohm  per  mile  after  two 
weeks'  submersion  in  water  at  70  degrees  Fahrenheit,  and  three  days'  submersion 
in  lime  water,  with  a  current  of  550  volts,  and  after  three  minutes'  electrification. 

A  wire  with  an  insulating  covering  that  will  not  support  combustion,  will  resist 
abrasion,  is  at  least  tle  of  an  inch  in  thickness,  and  thoroughly  impregnated  with 
a  moisture  repellant,  will  be  approved  for  outside  overhead  conductors,  except 
service  wires. 

b.  Must  be  so  placed  that  moisture  cannot  form  a  cross  con- 
nection between  them,  not  less  than  a  foot  apart,  and  not  in  con- 
tact with  any  substance  other  than  their  insulating  supports 

c.  Must  be  at  least  seven  feet  above  the  highest  point  of  flat 
roofs,  and  at  least  one  foot  above  the  ridge  of  pitched  roofs  over 
which  they  pass  or  to  which  they  are  attached. 

d.  Must   be   protected    by  dead  insulated  guard  irons  or 
cvires  from  possibility  of  contact  with  other  conducting  wires  or 
substances  to  which  current  may  leak.     Special  precautions  of 
this  kind  must  be  taken  where  sharp  angles  occur,  or  where  any 
wires  might  possibly  come  in  contact  with  electric  light  or  power 
w'ires. 

e.  Must  be  provided  with  petticoat  insulators  of  glass  or  por- 
celain.    Porcelain  knobs  or  cleats  and  rubber  hooks  will  not  be 
approved. 

f.  Must  be  so  spliced  or  jointed  as  to  be  both  mechanically 
and  electrically  secure  without  solder.  The  joints  must  then  be 
soldered,  to  insure  preservation,  and  covered  with  an  insulation 
equal  to  that  on  the  conductors. 

All  joints  must  be  soldered,  even  if  made  with  the  Mclntyre  or  any  other 
patent  splicing  device.  This  ruling  applies  to  joints  and  splices  in  all  classes  of 
wiring  covered  by  these  rules. 


206  ,      RULES  AND  REQUIREMENTS  OF  THE 

,fr.  Telegraph,  telephone  and  similar  wires  must  not  be  placed 
on  the  same  cross-arm  with  electric  light  or  power  wires. 

n.     SERVICE  BLOCKS: — 

Must  be  covered  over  their  entire  surface  with  at  least  two 
coats  of  waterproof  paint. 

12.     ALL  INTERIOR  CONDUCTORS: — 

a.  Must  be  covered  where  they  enter  buildings  from  outside 
terminal  insulators  to  and  through  the  walls  with  extra  waterproof 
insulation  and  must  have  drip  loops  outside.     The  hole  through 
which  the  conductor  passes  must  be  bushed  with  waterproof  and 
non-combustible   insulating   tube,    slanting  upwards   toward  the 
inside.     The  tube  must  be  sealed  with  tape,  thoroughly  painted, 
and  securing  the  tube  to  the  wire. 

b.  Must  be  arranged  to  enter  and  leave  the  building  through  a 
double-contact   service  switch,    which  will   effectually  close  the 
main  circuit  and  disconnect  the  interior  wires  when  it  is  turned 
"off."     The  switch  must  be  so  constructed  that  it  shall  be  auto- 
matic in  its  action,  not  stopping  between  points  when  started,  and 
prevent  an  arc  between   the  points  under  all  circumstances;  it 
must  indicate  on  inspection  whether  the  current  be  "  on  "  or  "  off, " 
and  be  mounted  in  a  non-combustible  case,  and  kept  free  from 
moisture,   and  easy   of   access  to  police  or  firemen.      So-called 
"  snap  switches"  shall  not  be  used  on  a  high  potential  system. 

c.  Must  be  always  in  plain  sight,  and  never  encased,  except 
when  required  by  the  Inspector. 

d      Must  have  an  approved  insulating  covering. 

Insulation  that  will  be  approved  for  interior  conductors  must  be  solid,  at  least 
-£i  of  an  inch  in  thickness  and  covered  with  a  substantial  braid.  It  must  not  read- 
ily carry  fire,  must  show  an  insulating  resistance  of  one  megohm  per  mile  after 
two  weeks'  submersion  in  water  at  70  degrees  Fahrenheit,  and  three  days'  sub- 
mersion in  lime  water,  with  a  current  of  550  volts,  and  after  three  minutes'  elec- 
trification. 

e.  Must  be  supported  on  glass  or  porcelain  insulators,  and 
kept  rigidly  at  least  eight  inches  from  each  other,  except  within 
the  structure  of  lamps  or  on  hanger-boards,  cut-out  boxes,  or  the 
like,  where  less  distance  is  necessary. 

f.  Must  be  separated  from  contact  with  walls,  floors,  timbers 
or  partitions  through  which  they  may  pass  by  non-combustible, 
non-absorptive,  insulating  tubes,  such  as  glass  or  porcelain. 

g.  Must  be  so  spliced  or  joined  as  to  be  both  mechanically  and 
electrically  secure  without  solder.     They  must  then  be  soldered, 
to  insure  preservation,  and  covered  with  an  insulation  equal  to 
that  on  the  conductors. 

All  joints  must  be  soldered,  even  if  made  with  the  Mclntyre  or  any  other 
patent  splicing  device.  This  ruling  applies  to  joints  and  splices  in  all  classes  of 
wiring  covered  by  these  rules. 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.          207 

h.  Must  be  protected  from  mechanical  injury,  when  necessary 
on  side  walls,  by  a  substantial  boxing,  retaining  an  air  space  of 
one  inch  around  the  conductors,  closed  at  the  top,  and  extending 
not  less  than  five  feet  from  the  floor.  Where  crossing  exposed 
floor  timbers  in  cellars  or  rooms,  the  conductors  must  be  attached 
by  their  insulating  supports  to  the  under  side  of  a  wooden  strip 
not  less  than  one-half  an  inch  in  thickness. 

LAMPS   AND    OTHER    DEVICES. 

13.     ARC  LAMPS — In  every  case: — 

a.  Must  be  carefully  isolated  from  inflammable  material., 

b.  Must  be  provided  at  all  times  with  a  glass  globe  surround- 
ing the  arc,  securely  fastened  upon  a  closed  base.      No  broken  or 
cracked  globes  to  be  used. 

c.  Must  be  provided  with  an  approved  hand-switch,  also  an 
automatic  switch  that  will  shunt  the  current  around  the  carbons 
should  they  fail  to  feed  properly. 

The  hand-switch  to  be  approved,  if  placed  anywhere  except  on  the  lamp 
itself,  must  comply  with  requirements  for  switches  on  hanger-boards  as  laid  down 
in  Section  £•  of  Rule  13. 

d.  Must  be  provided  with  reliable  stops  to  prevent  carbons 
from  falling  out  in  case  the  clamps  become  loose. 

e.  Must  be  carefully  insulated  from  the  circuit  in  all  their 
exposed  parts. 

/.  Must  be  provided  with  a  wire  netting  (having  a  mesh  not 
exceeding  one  and  one-quarter  inches)  around  the  globe,  and  an 
approved  spark  arrester  above,  to  prevent  escape  of  sparks, 
melted  copper  or  carbon,  where  readily  inflammable  material  is 
in  the  vicinity  of  the  lamps.  It  is  recommended  that  plain  car- 
bons, not  copper-plated,  be  used  for  lamps  in  such  places. 

An  approved  spark  arrester  is  one  which  will  so  close  the  upper  orifice  of  the 
globe  that  it  will  be  impossible  for  any  sparks  thrown  off  by  the  carbons  to 
escape. 

Arc  lamps,  when  used  in  places  where  they  are  exposed  to  flyings  of  easily 
inflammable  material,  should  have  the  carbons  enclosed  completely  in  a  globe  in 
such  manner  as  to  avoid  the  necessity  for  spark  arresters.  For  the  present,  spark 
arresters  will  not  be  required  on  so-called  "  inverted  arc  "  lamps. 

g.  Hanger-boards  must  be  so  constructed  that  all  wires  and 
current-carrying  devices  thereon  shall  be  exposed  to  view  and 
thoroughly  insulated  by  being  mounted  on  a  non-combustible, 
non-absorptive,  insulating  substance.  All  switches  attached  to 
the  same  must  be  so  constructed  that  they  shall  be  automatic  in 
their  action,  cutting  off  both  poles  to  the  lamp,  not  stopping 
between  points  when  started,  and  preventing  an  arc  between 
points  under  all  circumstances. 


2O8       RULES  AND  REQUIREMENTS  OF  THE 

h.  Where  hanger-boards  are  not  used,  lamps  to  be  hung  from 
insulated  supports  other  than  their  conductors. 

14.  INCANDESCENT  LAMPS  IN  SERIES  CIRCUITS  HAVING  A  MAXI- 
MUM POTENTIAL  OF  300  VOLTS  OR  OVER: — 

a.  Must  have  the  conductors  installed  as  provided  in  Rule  12, 
and  each  series  lamp  must  be  provided  with  an  automatic  cut-out. 

b.  Must  have  each  lamp  suspended  from  a  hanger-board  by 
means  of  rigid  tubes. 

c.  No  electro-magnetic  device  for  switches  and  no  system  of 
multiple-series  or  series-multiple  lighting  will  be  approved. 

d.  Under  no  circumstances  can  series  lamps  be  attached  to 
gas  fixtures. 

CLASS  C,  LOW  POTENTIAL  SYSTEMS. 
(300  VOLTS  OR  LESS.) 
OUTSIDE  CONDUCTORS. 

15.  OUTSIDE  OVERHEAD  CONDUCTORS: — 

a.  Must  be  erected  in  accordance  with   the   rules  for   high 
potential  conductors. 

b.  Must  be  separated  not  less  than  twelve  inches,  and  be  pro- 
vided with  an  approved  fusible  cut-out,  that  will  cut  off  the  entire 
current  as  near  as  possible  to  the  entrance  to  the  building  and 
inside  the  walls. 

An  approved  fusible  cut-out  must  comply  with  the  sections  of  Rules  23  and 
24,  describing  fuses  and  cut-outs.  The  cut-out  required  by  this  section  must  be 
placed  so  as  to  protect  the  switch  required  by  Rule  17. 

16.  UNDERGROUND  CONDUCTORS: — 

a.  Must  be  protected,  when  brought  into  a  building,  against 
moisture  and  mechanical  injury,  and  all  combustible   material 
must  be  kept  removed  from  the  immediate  vicinity. 

b.  Must  have  a  switch  and  a  cut-out  for  each  wire  between  the 
underground  conductors  and  the  interior  wiring  when   the  two 
parts  of  the  wiring  are  connected. 

These  switches  and  fuses  must  be  placed  as  near  as  possible  to 
the  end  of  the  underground  conduit,  and  connected  therewith  by 
specially  insulated  conductors,  kept  apart  by  not  less  than  two 
and  one-half  inches. 

The  cut-out  required  by  this  section  must  be  placed  so  as  to  protect  the 
switch. 

c.  Must  not  be  so  arranged  as  to  shunt  the  current  through  a 
building  around  any  catch  box. 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.         209 


INSIDE    WIRING.       GENERAL    RULES. 

17.  At  the  entrance  of  every  building  there  shall  be  an 
approved  switch  placed  in  the  service  conductors  by  which  the 
current  may  be  entirely  cut  off. 

The  switch  required  by  this  rule,  to  be  approved,  must  be  of  such  construc- 
tion that  each  wire  entering  the  building  will  be  disconnected  when  the  switch  is 
open,  must  plainly  indicate  whether  the  current  is  "on"  or  "off,"  and  must  com- 
ply with  sections  a,  c,  d  and  e  of  Rule  26,  relating  to  switches. 

18.  CONDUCTORS: — 

a.  Must  have  an  approved  insulating  covering,  and  must  not 
be  of  sizes  smaller  than  No.  14  B.  &  S.,  No.  16  B.  W.  G.  or  No.  4 
E.  S.  G.,  except  as  allowed  under  Rule  27  (d)  and  31  (a). 

In  so-called  "  concealed"  wiring,  moulding  and  conduit  work,  and ^in  places 
liable  to  be  exposed  to  dampness,  the  insulating  covering  of  the  wire,  to  be 
approved,  must  be  solid,  at  least  ^  of  an  inch  in  thickness,  and  covered  with  a 
substantial  braid.  It  must  not  readily  carry  fire;  must  show  an  insulating  resist- 
ance of  one  megohm  per  mile  after  two  weeks'  submersion  in  water  at  70  degrees 
Fahrenheit,  and  three  days'  submersion  in  lime  water,  with  a  current  of  550  volts, 
and  after  three  minutes'  electrification. 

For  work  which  is  entirely  exposed  to  view  throughout  the  whole  interior 
circuits,  and  not  liable  to  be  exposed  to  dampness,  a  wire  with  an  insulation  cov- 
ering thatwill  not  support  combustion,  will  resist  abrasion,  is  at  least  A  of  an  inch 
in  thickness  and  thoroughly  impregnated  wfth  a  moisture  repellant,  will  be 
approved. 

b.  Must  be  protected  when  passing  through  floors,  walls,  par- 
titions,  timbers,  etc.,  by  non-combustible,   non-absorptive,  insu- 
lating tubes,  such  as  glass  or  porcelain. 

c.  Must  be  kept  free  from  contact  with  gas,  water  or  other 
metallic  piping,  or  any  other  conductors  or  conducting  material 
which  they  may  cross,  by  some  continuous  and  firmly  fixed  non- 
conductor, creating  a  separation  of  at  least  one  inch.     Deviations 
from  this  rule  may  sometimes  be  allowed  by  special  permission. 

d.  Must  be  so  placed  in  wet  places  that  an  air  space  will  be 
left  between  conductors  and  pipes  in  crossing,  and  the  former 
must  be  run  in  such  a  way  that  they  cannot  come  in  contact  with 
the  pipe  accidentally.     Wires  should  be  run  over  all  pipes  upon 
which  moisture  is  liable  to  gather,  or  which  by  leaking  might 
cause  trouble  on  a  circuit. 

e.  Must  be  so  spliced  or  joined  as  to  be  both  mechanically  and 
electrically  secure  without  solder.     They  must  then  be  soldered, 
to  insure  preservation,  and  covered  with  an  insulation  equal  to 
that  on  the  conductors. 

All  joints  must  be  soldered,  even  if  made  with  the  Mclntyre  or  any  other 
patent  splicing  device.  This  ruling  applies  to  joints  and  splices  in  all  classes  of 
wiring  covered  by  these  rules. 

f.  Must  be  protected  from  mechanical  injury,  when  necessary 
on  side  walls,  by  a  substantial  boxing,  retaining  an  air  space  of 


210       RULES  AND  REQUIREMENTS  OF  THE 

one  inch  around  the  conductors,  closed  at  the  top,  and  extending 
not  less  than  five  feet  from  the  floor,  or  by  an  iron-armored  or 
metal-sheathed  insulating  conduit  sufficiently  strong  to  withstand 
the  strain  it  will  be  subjected  to,  the  inner  insulating  tubing  to 
extend  one-half  inch  beyond  the  ends  of  the  metal  tube,  which 
must  extend  not  less  than  five  feet  from  the  floor.  Where  cross- 
ing exposed  floor  timbers  in  cellars  or  rooms,  the  conductors  must 
be  attached  by  their  insulating  supports  to  the  under  side  of  a 
wooden  strip  not  less  than  one-half  inch  in  thickness  and  not  less 
than  three  inches  in  width. 

SPECIAL  RULES. 
19.  WIRING  NOT  INCASED  IN  MOULDING  OR  APPROVED  CONDUIT: — 

a.  Must  be  supported  wholly  on  non-combustible  insulators, 
constructed  so  as  to  prevent  the  insulating  coverings  of  the  wire 
from  coming  in  contact  with  other  substances  than  the  insulating 
supports. 

b.  Must  be  so  arranged  that  wires  of  opposite  polarity,  with  a 
difference  of  potential  of  150  volts  or  less,  will  be  kept  apart  at 
least  two  and  one-half  inches. 

c.  Must  have   the  above  distance  increased   proportionately 
where  a  higher  voltage  is  used. 

d.  Must  not  be  laid  in  plaster,  cement  or  similar  finish. 

e.  Must  never  be  fastened  with  staples. 

IN    UNFINISHED    LOFTS,    BETWEEN    FLOOR    AND    CEILINGS,    IN    PARTI- 
TIONS  AND    OTHER    CONCEALED    PLACES. 

f.  Must  have  at  least  one  inch  clear  air  space  surrounding 
them. 

g-.  Must  be  at  least  ten  inches  apart  when  possible,  and  should 
be  run  singly  on  separate  timbers  or  studding. 

h.  Wires  run  as  above  immediately  under  roofs,  in  proximity 
to  water  tanks  or  pipes,  will  be  considered  as  exposed  to 
moisture. 

i.  When  from  the  nature  of  the  case  it  is  impossible  to  place 
concealed  wire  on  non-combustible  insulating  supports  of  glass  or 
porcelain,  the  wires  may  be  fished  on  the  loop  system,  if  encased 
throughout  in  approved  continuous  flexible  tubing  or  conduit. 

American  Circular  Loom  Tubing  is  approved  for  use  under  this  rule. 

j.  Wires  must  not  be  fished  for  any  great  distance,  and  only  in 
places  where  the  Inspector  can  satisfy  himself  that  the  above 
rules  have  been  complied  with. 

k.  Twin  wires  must  never  be  employed  in  this  class  of  con- 
cealed work. 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.          211 

20.  MOULDINGS: — 

a    Must  never  be  used  in  concealed  work  or  in  damp  places. 

b.  Must  have,   both  outside  and  inside,  at  least  two  coats  of 
waterproof  paint,  or  be  impregnated  with  a  moisture  repellant. 

c.  Must  be  made  of  two  pieces,  a  backing  and  capping,  so  con- 
structed as  to  thoroughly  encase  the  wire  and  provide  a  one-half 
inch  tongue   between  conductors    and  a  solid  backing,    which, 
under  grooves,  shall  not  be  less  than  three-eighths  of  an  inch  in 
thickness,  and  must  afford  suitable  protection  from  abrasion. 

It  is  recommended  that  only  hardwood  moulding  be  used. 

21.  SPECIAL  WIRING: — 

In  breweries,  packing-houses,  stables,  dye-houses,  paper  and 
pulp  mills,  or  other  buildings  specially  liable  to  moisture  or  acid, 
or  other  fumes  liable  to  injure  the  wires  or  insulation,  except 
where  used  for  pendants,  conductors  — 

a.  Must  be  separated  at  least  six  inches,  and  should  have  no 
joints  or  splices. 

b.     Must  be  provided  with  an  approved  insulating  covering. 

The  insulating  covering  of  the  wire  to  be  approved  under  this  section  must  be 
solid,  at  least  A;  of  an  inch  in  thickness  and  covered  with  a  substantial  braid.  It 
must  not  readily  carry  fire,  must  show  an  insulating  resistance  of  one  megohm 
per  mile  after  two  weeks'  submersion  in  water  at  70  degrees  Fahrenheit,  and 
three  days'  submersion  in  lime  water,  with  a  current  of  550  volts,  after  three  min- 
utes' electrification,  and  must  also  withstand  a  satisfactory  test  against  such  chem- 
ical compounds  or  mixtures  as  it  will  be  liable  to  be  subjected  to  in  the  risk  under 
consideration. 

c.  Must  be  carefully  put  up. 

d.  Must  be  supported  by  glass  or  porcelain  insulators.     No 
switches,   key-sockets  or  fusible  cut-outs  will  be  allowed  where 
exposed  to  inflammable  gases  or  dust,  or  to  flyings  of  combustible 
material.     In  damp  places  switches  and  cut-out  blocks  must  be 
mounted  on  porcelain  knobs. 

e.  Must  be  protected  when  passing  through  floors,  walls,  par- 
titions,  timbers,   etc.,   by  non-combustible,  non-absorptive,   insu- 
lating tubes,  such  as  glass  or  porcelain. 

22.  INTERIOR  CONDUITS*: — 

The  American  Circular  Loom  Company  Tube,  the  brass-sheathed  and  the 
iron-armored  tubes  made  by  the  Interior  Conduit  and- Insulation  Company,  the 
iron-armored  tube  made  by  the  Builders'  Insulating  Tube  Company,  of  Lynn, 
Mass.,  the  iron-armored  tube  made  by  the  Clifton  Mfg.  Co.,  of  Boston,  and  the 
Vulca  Tube,  are  approved  for  the  class  of  work  called  for  in  this  rule. 

a.  Must  be  continuous  from  one  junction  box  to  another,  or 
to  fixtures,  and  must  be  of  material  that  will  resist  the  fusion  of 
the  wire  or  wires  they  contain  without  igniting  the  conduit. 

*The  object  of  a  tube  or  conduit  is  to  facilitate  the  insertion  or  extraction  of 
the  conductors,  to  protect  them  from  mechanical  injury,  and,  as  far  as  possible, 
from  moisture.  Tubes  or  conduits  are  to  be  considered  merely  as  raceways,  and 
are  not  to  be  relied  on  for  insulation  between  wire  and  wire,  or  between  the  wire 
and  the  ground. 


212        RULES  AND  REQUIREMENTS  OF  THE 

b.  Must  not  be  of  such  material  or  construction  that  the  insu- 
lation of  the  conductor  will  ultimately  be  injured  or  destroyed  by 
the  elements  of  the  composition. 

c.  Must  be  first  installed  as  a  complete  conduit  system,  with- 
out the  conductors,  which  must  not  be  drawn  in  until  all  mechan- 
ical work  on  the  building  has  been,  as  far  as  possible,  completed. 

d.  Must   not   be  so  placed  as  to  be  subject    to   mechanical 
injury  by  saws,  chisels  or  nails. 

e.  Must  not  be  supplied  with  a  twin  conductor  or  two  separate 
conductors  in  a  single  tube,  except  in  an  approved  iron  or  steel- 
armored  conduit. 

The  use  of  approved  wires  of  opposite  polarity,  either  separate  or  twin  con- 
ductor, in  a  straight  conduit  installation,  is  allowed  in  approved  iron-armored  or 
steel-armored  conduits,  but  not  in  any  of  the  other  approved  conduits. 

Iron  or  steel-armored  conduit  to  be  approved  must  fulfill  the  following  speci- 
fications: 

1.  Must  not  be  seriously  affected  externally  by  burning  out  a  wire  inside  the 
tube  when  the  iron  pipe  is  connected  to  one  side  of  the  circuit. 

2.  When  bent  with  a  sag  of  one  foot  in  the  middle  of  a  ten-foot  length,  and 
filled  with  water,  must  have  an  insulation  resistance  between  the  water  and  the 
iron  pipe  of  one  megohm  after  three  days,  temperature  being  21  degrees  Centi- 


jrade  (70  degrees  Fahrenheit). 
3.  The  i 


3.  The  insulating  material  removed  from  the  tube  must  not  absorb  more  than 
ten  per  cent.,  by  weight,  of  water  after  one  weeks'  immersion. 

4.  The  insulating  material  must  not  soften  at  a  temperature  below  70  degrees 
Centigrade  ^158  degrees  Fahrenheit),  and   must  leave  the  water  in  which  it  is 
boiled  practically  neutral. 

5.  The  insulating  material  must  not  become  mechanically  weak  after  three 
days'  immersion  in  water. 

f.  Must  have  all  ends  closed  with  good  adhesive  material,  either 
at  junction  boxes  or  elsewhere,  whether  such  ends  are  concealed 
or  exposed.     Joints  must  be  made  air-tight  and  moisture-proof. 

g.  Conduits  must  extend  at  least  one  inch  beyond  the  finished 
surface  of  walls  or  ceilings  until  the  mortar  or  other  similar  mate- 
rial be  entirely  dry,  when   the  projection  may  be  reduced  to  half 
an  inch. 

23.     DOUBLE-POLE  SAFETY  CUT-OUTS: — 

a.  Must  be  in  plain  sight  or  inclosed  in  an  approved  box,  and 
readily  accessible.     They  must  not  be  placed  in  the  canopies  or 
shells  of  fixtures. 

To  be  approved  boxes  must  be  constructed,  and  cut-outs  arranged,  whether  in 
a  box  or  not,  so  as  to  obviate  any  danger  of  the  melted  fuse  metal  coming  in  con- 
tact with  any  substance  which  might  be  ignited  thereby. 

b.  Must  be  placed  at  every  point  where  a  change  is  made  in 
the  size  of  the  wire  (unless  the  cut-out  in  the  larger  wire  will  pro- 
tect the  smaller). 

c.  Must  be  supported  on  bases  of  non-combustible,  insulating, 
moisture-proof  material. 

d.  Must  be  supplied  with  a  plug  (or  other  device  for   inclosing 
the  fusible  strip  or  wire)  made  of  non-combustible  and  moisture- 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.         213 

proof  material,  and  so  constructed  that  an  arc  cannot  be  main- 
tained across  its  terminals  by  the  fusing  of  the  metal. 

e .  Must  be  so  placed  that  no  set  of  lamps,  whether  grouped  on 
one  fixture  or  on  several  fixtures  or  pendants,  requiring  a  current 
of  more  than  six  amperes,  shall  be  ultimately  dependent  upon  one 
cut-out.  Special  permission  may  be  given  in  writing  by  the 
Inspector  for  departure  from  this  rule  in  case  of  large  chandeliers. 

24.  SAFETY  FUSES: — 

a.  Must  all  be  stamped  or  otherwise  marked  with  the  maximum 
number  of  amperes  they  will  carry  indefinitely  without  melting. 

b.  Must  have  fusible  wires  or  strips  (where  the  plug  or  equiv- 
alent device  is  not  used),  with  contact  surfaces  or  tips  of  harder 
metal,  soldered  or  otherwise,  having  perfect  electrical  connection 
with  the  fusible  part  of  the  strip. 

c.  Must  all  be  so  proportioned   to   the   conductors  they  are 
intended  to  protect  that  they  will  melt  before  the  maximum  safe- 
carrying  capacity  of  the  wire  is  exceeded. 

25.  TABLE  OF  CAPACITY  OF  WIRES: — 

It  must  be  clearly  understood  that  the  size  of  the  fuse  depends 
upon  the  size  of  the  smallest  conductor  it  protects  and  not  upon 
the  amount  of  current  to  be  used  on  the  circuit.  Below  is  a  table 
showing  the  safe  carrying  capacity  of  conductors  of  different  sizes 
in  Brown  &  Sharpe  gauge,  which  must  be  followed  in  the  placing 
of  interior  conductors: — 

TABLE  A,   CONCEALED  WORK.  TABLE  B,   OPEN  WORK. 

B.  &  S.  G.  Amperes.  Amperes. 

OOOO 


)00  

181  

262 

oo.  

150  

220 

o  

125  

185 

I  

.  .  105  .  . 

i  *\6 

2  

88  

i3i 

3  , 

75  

no 

Q2 

C2 

11 

6  

,  45  

65 

8  

,  33  

,.  46 

10  

,  25  

12  

17  

2_ 

14 

,  .  .    ...   12 

16 

16  

6  

8 

18.. 

3.  . 

«; 

NOTE. — By  "  open  work"  is  meant  construction  which  admits  of  all  parts  of 
the  surface  of  the  insulating  covering  of  the  wire  being  surrounded  by  free  air. 
The  carrying  capacity  of  16  and  18  wire  is  given,  but  no  wire  smaller  than  14  is  to 
be  used,  except  allowed  under  Rules  27  (d)  and  31  (a). 


214  RULES    AND    REQUIREMENTS    OF   THE 

26.  SWITCHES:  — 

a.  Must  be  mounted  on  moisture-proof  and  non-combustible 
bases,  such  as  slate  or  porcelain. 

b.  Must  be  double  pole  when  the  circuits  which  they  control 
supply  more  than  six  16  candle-power  lamps,  or  their  equivalent. 

c.  Must  have  a  firm  and  secure  contact;  must  make  and  break 
readily,  and  not  stop  when  motion  has  once  been  imparted  by  the 
handle. 

d.  Must  have  carrying  capacity  sufficient  to  prevent  heating. 

e.  Must  be  placed  in  dry,  accessible  places,  and  be  grouped  as 
far  as  possible,  being  mounted — when  practicable — upon  slate  or 
equally  non-combustible  back  boards.   Jackknife  switches,  whether 
provided  with  friction  or  spring  stops,  must  be  so  placed  that 
gravity  will  tend  to  open  rather  than  close  the  switch. 

27.  FIXTURE  WORK: — 

a.  In  all  cases  where   conductors   are   concealed    within  or 
attached  to  gas  fixtures,  the  latter  must  be  insulated  from  the  gas- 
pipe  system  of   the  building  by   means  of  approved  insulating 
joints  placed  as  close  as  possible  to  the  ceiling. 

Insulating  joints  with  soft  rubber  in  their  construction  will  not  be  approved. 
It  is  recommended  that  the  gas-outlet  pipe  be  protected  above  the  insulating 
joint  by  a  non-combustible,  non-absorptive  insulating  tube  having  a  flange  at  the 
lower  end,  where  it  comes  in  contact  with  the  insulating  joint,  and  that,  where 
outlet  tubes  are  used,  they  be  of  sufficient  length  to  extend  below  the  joint,  and 
that  they  be  so  secured  that  they  will  not  be  pushed  back  when  the  canopy  is  put 
in  place.  Where  iron  ceilings  are  used  care  must  be  taken  to  see  that  the  canopy 
is  thoroughly  and  permanently  insulated  from  the  ceiling. 

Insulating  joints  to  be  approved  must  be  entirely  made  of  material  that  will 
resist  the  action  of  illuminating  gases,  and  will  not  give  way  or  soften  under  the 
heat  of  an  ordinary  gas  flame.  They  shall  be  so  arranged  that  a  deposit  of 
moisture  will  not  destroy  the  insulating  effect,  and  shall  have  an  insulating  resist- 
ance of  250,000  ohms  between  the  gas-pipe  attachments,  and  be  sufficiently  strong 
to  resist  the  strain  they  will  be  liable  to  in  attachment. 

b.  Supply  conductors,    and  especially  the   splices    to  fixture 
wires,  must  be  kept  clear  of  the  grounded  part  of  gas  pipes,  and 
where  shells  are  used,  the  latter  must  be  constructed  in  a  manner 
affording  sufficient  area  to  allow  this  requirement. 

c.  When  fixtures  are  wired  outside,  the  conductors  must  be  so 
secured  as  not  to  be  cut  or  abraded  by  the  pressure  of  the  fasten- 
ings or  motion  of  the  fixture. 

d.  All  conductors  for  fixture  work  must  have  a  waterproof 
insulation  that  is  durable  and  not  easily  abraded,  and  must  not  in 
any  case  be  smaller  than  No.  18  B.  &  S.,  No.  20  B.  W.  G.,  No.  2 
E.  S.  G. 

e.  All  burs  or  fins  must  be  removed  before  the  conductors  are 
drawn  into  a  fixture. 

/.  The  tendency  to  condensation  within  the  pipes  should  be 
guarded  against  by  sealing  the  upper  end  of  the  fixture. 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.         215 

g.  No  combination  fixture  in  which  the  conductors  are  con- 
cealed in  a  space  less  than  one-fourth  inch  between  the  inside 
pipe  and  the  outside  casing  will  be  approved. 

h.  Each  fixture  must  be  tested  for  "contacts"  between  con- 
ductors and  fixtures,  for  "short  circuits,"  and  for  ground  connec- 
tions before  the  fixture  is  connected  to  its  supply  conductors. 

i.  Ceiling  blocks  of  fixtures  should  be  made  of  insulating  mate- 
rial; if  not,  the  wires  in  passing  through  the  plate  must  be  sur- 
rounded with  hard-rubber  tubing. 

28.  ARC  LIGHTS  ON  Low  POTENTIAL  CIRCUITS: — 

a.  Must  be  connected  with  main  conductors  only  through  a 
double-pole  cut-out  and  a  double-pole  switch,  which  shall  plainly 
indicate  whether  "on"  or  "off." 

b.  Must  only  be  furnished  with  such  resistances  or  regulators 
as  are  inclosed   in    non-combustible   material,    such    resistances 
being  treated  as  stoves.    Incandescent  lamps  must  not  be  used  for 
resistance  devices. 

c.  Must  be  supplied  with  globes  and  protected  as  in  the  case 
of  arc  lights  on  high-potential  circuits. 

29.  ELECTRIC  GAS  LIGHTING: — 

Where  electric  gas  lighting  is  to  be  used  on  the  same  fixture 
with  the  electric  light — 

a.  No  part  of  the  gas  piping  or  fixture  shall  be  in  electrical 
connection  with  the  gas-lighting  circuit. 

b.  The  wires  used  with   the  fixtures  must  have  a  non-inflam- 
mable insulation,  or,  where  concealed  between  the  pipe  and  shell 
of  the  fixture,  the  insulation  must  be  such  as  required  for  fixture 
wiring  for  the  electric  light. 

c.  The  whole  installation  must  test  free  from  "grounds." 

d  The  two  installations  must  test  perfectly  free  from  connec- 
tion with  each  other. 

30.  SOCKETS: — 

a.  No  portion  of  the  lamp  socket  exposed  to  contact  with  out- 
side objects  must  be  allowed  to  come  into  electrical  contact  with 
either  of  the  conductors. 

b.  In  rooms  where  inflammable  gases  may  exist,  or  where  the 
atmosphere  is  damp,  the  incandescent  lamp  and  socket  should  be 
inclosed  in  a  vapor-tight  globe. 

31.  FLEXIBLE  CORD: —  , 
a.  Must  be  made  of  two- stranded  conductors,  each  having  a 

carrying  capacity  equivalent  to  not  less  than  a  No.  16  B.  &  S. 
wire,  and  each  covered  by  an  approved  insulation,  and  protected 
by  a  slow-burning,  tough,  braided  outer  covering. 


2l6       RULES  AND  REQUIREMENTS  OF  THE 

Insulation  ior  pendants  under  this  rule  must  be  moisture  and  flame-proof. 

Insulation  for  fixture  work  must  be  waterproof,  durable  and  not  easily 
abraded. 

Insulation  for  cords  used  for  all  other  purposes,  including  portable  lamps  and 
motors,  must  be  solid,  at  least  ^  of  an  inch  in  thickness,  and  must  show  an  insu- 
lation resistance  between  conductors  and  between  either  conductor  and  the 
ground  of  at  least  one  megohm  per  mile,  after  one  week's  immersion  in  water 
at  70  degrees  Fahrenheit,  with  a  current  of  550  volts,  and  after  three  minutes' 
electrification. 

b.  Must  not  sustain  more  than  one  light  not  exceeding  50 
candle-power. 

c.  Must  not  be  used  except  for  pendants,  wiring  of  fixtures 
and  portable  lamps  or  motors. 

d.  Must  not  be  used  in  show  windows. 

e.  Must  be  protected  by  insulating  bushings  where  the  cord 
enters  the  socket.    The  ends  of  the  cord  must  be  taped  to  prevent 
fraying  of  the  covering. 

f.  Must  be  so  suspended  that  the  entire  weight  of  the  socket 
and  lamp  will  be  borne  by  knots  under  the  bushing  in  the  socket, 
and  above  the  point  where  the  cord  comes   through  the  ceiling 
block  or  rosette,  in  order  that  the  strain  may  be  taken  from  the 
joints  and  binding  screws. 

g.  Must  be  equipped  with  keyless  sockets  as  far  as  practica- 
ble, and  be  controlled  by  wall  switches. 

32.  DECORATIVE  SERIES  LAMPS: — 

Incandescent  lamps  run  in  series  circuits  shall  not  be  used  for 
decorative  purposes  inside  of  buildings,  except  by  special  permis- 
sion in  writing  from  the  Underwriters  having  jurisdiction. 

CLASS  D,  ALTERNATING  SYSTEMS. 
CONVERTERS.  OR  TRANSFORMERS. 

33.  CONVERTERS: — 

a.  Must  not  be  placed  inside  of  any  building,  except  the  Cen- 
tral Station,  unless  by  special  permission  of   the  Underwriters 
having  jurisdiction. 

b.  Must  not  be  placed  in  any  but  metallic  or  other  non-com- 
bustible cases. 

c.  Must  not  be  a'ttached  to  the  outside  walls  of  buildings,  unless 
separated  therefrom  by  substantial  insulating  support 

34.  IN  THOSE  CASES  WHERE  IT  MAY  NOT  BE  POSSIBLE  TO  EXCLUDE 
THE  CONVERTERS  AND  PRIMARY   WIRES  ENTIRELY  FROM  THE 

'BUILDING,  THE  FOLLOWING   PRECAUTIONS   MUST  BE  STRICTLY 

OBSERVED: — 

Converters  must  be  located  at  a  point  as  near  as  possible  to 
that  at  which  the  primary  wires  enter  the  building,  and  must  be 
placed  in  an  inclosure  constructed  of,  or  lined  with,  fire-resisting 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.          2iy 

material;  the  inclosure  to  be  used  only  for  this  purpose,  and  to 
be  kept  securely  locked,  and  access  to  the  same  allowed  only  to 
responsible  persons.  They  must  be  effectually  insulated  from 
the  ground,  and  the  inclosure  in  which  they  are  placed  must  be 
practically  air-tight,  except  that  it  shall  be  thoroughly  ventilated 
to  the  out-door  air,  if  possible,  through  a  chimney  or  flue.  There 
should  be  at  least  six  inches  air  space  on  all  sides  of  the  converter. 

35.  PRIMARY  CONDUCTORS: — 

a.  Must  each  be  heavily  insulated  with  a  coating  of  moisture- 
proof  material  from  the  point  of  entrance  to  the  transformer,  and, 
in  addition,  must  be  so  covered  and  protected  that  mechanical 
injury  to  them,  or  contact  with   them,  shall  be  practically  impos- 
sible. 

b.  Must  each  be  furnished,  if  within  a  building,  with  a  switch 
and  a  fusible  cut-out  where  the  wires  enter  the  building,  or  where 
they  leave  the  main  line.     These  switches  should  be  inclosed  in 
secure  and  fireproof  boxes,  preferably  outside  the  building. 

c.  Must  be  kept  apart  at  least  ten  inches,  and  at  the  same  dis- 
tance from  all  other  conducting  bodies  when  inside  a  building. 

36.  SECONDARY  CONDUCTORS: — 

Must  be  installed  according  to  the  rules  for  "Low- Potential 
Systems." 

CLASS  E,  ELECTRIC  RAILWAYS. 

37.  All  rules  pertaining  to   arc-light  wires   and   stations   shall 
apply  (so  far  as  possible)  to  street  railway  power  stations  and 
their  conductors  in  connection  with  them. 

38.  POWER  STATIONS: — 

Must  be  equipped  in  each  circuit  as  it  leaves  the  station  with 
an  approved  automatic  "breaker,"  or  other  device  that  will 
immediately  cut  off  the  current  in  case  the  trolley  wires  become 
grounded.  This  device  must  be  mounted  on  a  fireproof  base,  and 
in  full  view  and  reach  of  the  attendant. 

Automatic  circuit  breakers  should  be  submitted  for  approval  before  being 
used. 

39.  TROLLEY  WIRES  . — 

a.  Must  be  no  smaller  than  No   o  B.  &  S.  copper  or  No.  4  B. 
&  S.  silicon  bronze,  and  must  readily  stand  the  strain  put  upon 
them  when  in  use 

b.  Must  be  well  insulated  from  their  supports,  and  in  case  of 
the  side  or  double  pole  construction    the  supports  shall  also  be 
insulated  from  the  poles  immediately  outside  of   the  trolley  wire. 


2l8        RULES  AND  REQUIREMENTS  OF  THE 

c.  Must  be  capable  of  being  disconnected  at  the  power  house, 
or  of  being  divided  into  sections,  so  that  in  case  of  fire  on  the  rail- 
way route  the  current  may  be  shut  off  from  the  particular  section 
and  not  interfere  with  the  work  of  the  firemen.     This  rule  also 
applies  to  feeders. 

d.  Must  be  safely  protected  against  contact  with  all  other  con- 
ductors. 

40.  CAR  WIRING  : — 

Must  be  always  run  out  of  reach  of  the  passengers,  and  must 
be  insulated  with  a  waterproof  insulation 

41.  LIGHTING  AND  POWER  FROM  RAILWAY  WIRES  : — 

Must  not  be  permitted,  under  any  pretense,  in  the  same  cir- 
cuit with  trolley  wires  with  a  ground  return,  nor  shall  the  same 
dynamo  be  used  for  both  purposes,  except  in  street  railway  cars, 
electric  car  houses,  and  their  power  stations. 

42.  CAR  HOUSES  :  — 

a.  Must  have  the  trolley  wires  properly  supported  on  insulat- 
ing hangers. 

b.  Must  have  the  trolley  hangers  placed  at  such  a  distance 
apart  that  in  case  of  a  break  in  the  trolley  wire,  contact  cannot  be 
made  with  the  floor. 

c.  Must  have  cut-out  switch  located  at  a  proper  place  outside 
of  the  building,  so  that  all  trolley  circuits  in  the  building  can  be 
cut  out  at  one  point,  and  line  circuit  breakers  must  be  installed, 
so  that  when  this  cut-out  switch  is  open  the  trolley  wire  will  be 
dead  at  all  points  within  100  feet  of  the  building.     The  current 
must  be  cut  out  of  the  building  whenever  the  same  is  not  in  use, 
or  the  road  not  in  operation. 

d.  Must  have  all  lamps  and  stationary  motors  installed  in  such 
a  way  that  one  main  switch  can  control  the  whole  of  each  instal- 
lation (lighting  or  power),  independently  of  main  feeder  switch. 
No  portable  incandescent  lamps  or  twin  wire  allowed,  except  that 
portable  incandescent  lamps  maybe  used  in  the  pits  ;  connections 
to  be  made  by  two  approved  rubber-covered  flexible  wires,  prop- 
erly protected  against  mechanical  injury  ;  the  circuit  to  be  con- 
trolled by  a  switch  placed  outside  of  the  pit. 

e.  Must  have  all  wiring  and  apparatus  installed  in  accordance 
with  rules  under  Class  B. 

f.  Must  not  have  any  system  of  feeder  distribution  centering 
in  the  building. 

g.  Must  have  the  rails  bonded  at  each  joint  with  not  less  than 
No.  2  B.  &  S.  annealed  copper  wire  ;  also  a  supplementary  wire 
to  be  run  for  each  track. 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.          219 

h.   Must  not  have  cars  left  with  trolley  in  electrical  connection 
with  the  trolley  wire. 

43.  GROUND  RETURN  WIRES  : — 

Where  ground  return  is  used  it  must  be  so  arranged  that  no 
difference  of  potential  will  exist  greater  than  5  volts  to  50  feet,  or 
50  volts  to  the  mile  between  any  two  points  in  the  earth  or  pipes 
therein. 

CLASS  F,   ELECTRIC  HEATERS. 

44.  ELECTRIC  HEATERS: — 

a.  If  stationary,  must  be  placed  in  a  safe  situation,   isolated 
from  inflammable  materials  and  treated  as  stoves 

b.  Must   have  double-pole   indicating  switches    and  double- 
pole  cut-outs  arranged  as  required  for  electric   light  or  power  of 
same  potential  and  current. 

c.  Must  have  the  attachments  of  feed  wires  to  the  heaters  in 
plain  sight,   easily  accessible,  and  protected  from  interference, 
accidental  or  otherwise. 

d.  The   flexible   conductors   for  portable  apparatus,  such  as 
irons,  etc.,  must  have  an  insulation   that  will  not  be  injured  by 
heat,  such  as  asbestos,  which  must  be  protected  from  mechanical 
injury  by  an  outer  substantial  braided  covering,  and  so  arranged 
that  mechanical  strain  will  not  be  borne  by  the  electrical  con- 
nections. 

CLASS  G,  STORAGE  OR  PRIMARY  BATTERIES. 

45.  STORAGE  OR  PRIMARY  BATTERIES:— 

a.  When  current  for  light  and  power  is  taken  from  primary  or 
secondary   batteries,     the    same    general    regulations    must    be 
observed  as  applied  to  similar  apparatus  fed  from  dynamo  gen- 
erators developing  the  same  difference  of  potential. 

b.  All   secondary  batteries  must   be   mounted   on  a^roved 
insulators. 

Insulators   for   mounting   secondary  batteries,  to  be  approved,  must  be  non- 
combustible,  such  as  glass,  or  thoroughly  vitrified  and  glazed  porcelain. 

c.  Special  attention  is  directed  to  the  rules  for  rooms  where 
acid  fumes  exist. 

d.  The  use  of  any  metal  liable  to  corrosion  must  be  avoided 
in  connections  of  secondary  batteries. 

MISCELLANEOUS. 

46.  MISCELLANEOUS: — 

a.  The  wiring  in   any  building  must  test  free  from  grounds: 
i.  e.,  each  main  supply  line  and  every  branch  circuit  should  have 


22O       RULES  AND  REQUIREMENTS  OF  THE 

an  insulation  resistance  of  at  least  100,000  ohms,  and  the  whole 
installation  should  have  an  insulation  resistance  between  con- 
ductors and  between  all  conductors  and  the  ground  (not  including 
attachments,  sockets,  receptacles,  etc.)  of  not  less  than  the  fol- 
lowing:— 

Up  to     10  amperes 4,000,000 

25  "        1,600,000 

50  "        800,000 

' '       100  " 300,009 

200  "        160,000 

' '      400  "        80,  ooo 

"       800  "        22,000 

"    1, 600  "        11,000 

All  cut-outs  and  safety  devices  in  place  in  the  above. 

Where  lamp  sockets,   receptacles   and   electroliers,   etc.,   are 
connected,  one-half  of  the  above  will  be  required. 

b.  Ground  wires  for  lightning  arresters   of  all  classes,   and 
ground  detectors  must  not  be  attached  to  gas  pipes  within  the 
building. 

c.  Where  telephone,  telegraph  or  other  wires  connected  with 
outside  circuits  are  bunched  together   within  any    building,    or 
where  inside  wires  are  laid  in  conduit  or  duct  with  electric  light 
or  power  wires,  the  covering  of  such  wires  must  be  fire-resisting, 
or  else  the  wires  must  be  inclosed  in  an  air-tight  tube  or  duct. 

d.  All  aerial  conductors  and  underground  conductors,  which 
are  directly  connected  to  aerial  wires,  connecting  with  telephone, 
telegraph,   district  messenger,   burglar-alarm,   watch-clock,   elec- 
tric time  and  other  similar  instruments,  must  be  provided  near 
the  point  of  entrance  to  the  buildings  with  some  approved  pro- 
tective device  which   will  operate  to  shunt   the   instruments  in 
case  of  a  dangerous  rise  of  potential,  and  will  open  the  circuit  and 
arrest  an  abnormal  current  flow.     Any  conductor  normally  form- 
ing an  innocuous  circuit  may  become  a  source  of  fire  hazard  if 
crossed  with  another  conductor,    through  which  it  may  become 
charged  with  a  relatively  high  pressure. 

Protectors  must  have  a  non-combustible,  insulating  base,  and  the  cover  to  be 
provided  with  a  lock  similar  to  the  lock  now  placed  on  telephone  apparatus  or 
some  equally  secure  fastening,  and  to  be  installed  under  the  following  require-   t 
ments: — 

1.  The  protector  to  be  located  at  the  point  where  the  wires  enter  the  build- 
ing, either  immediately  inside  or  outside  of  the  same.     If  outside,  the  protector 
to  be  inclosed  in  a  metallic,  waterproof  case. 

2.  If  the  protector  is  placed  inside  of  building,  the  wires  of  the  circuit  from 
the  support  outside  to  the  binding  posts  of  the  protector  to  be  of  such  insulation  as 
is  approved  for  service  wires  of  electric  light  and  power,  and  the  holes  through  the 
outer  walls  to  be  protected  by  bushing  the  same  as  required  for  electric  light  and 
power-service  wires. 


NATIONAL    BOARD    OF    FIRE    UNDERWRITERS.  221 

3.  The  wire  from  the  point  of  entrance  to  the  protector  to  be  run  in  accord- 
ance with  rules  for  high  potential  wires:  i.  e.,  free  of  contact  with  building  and 
supported  on  non-combustible  insulators. 

4.  The  ground  wire  shall  be  insulated,    not   smaller  than  No.  16  B.  &  S. 
gauge.     This  ground  wire  shall  be  kept  at  least  three  (3)  inches  from  all  conduc- 
tors, and  shall  never  be  secured  by  uninsulated  double-pointed  tacks. 

5.  The  ground  wire  shall  be  attached  to  a  water  pipe,  if  possible;  otherwise 
may  be  attached  to  a  gas  pipe.    The  ground  wire  shall  be  carried  to  and  attached 
to  the  pipe  outside  of  the  first  joint  or  coupling  inside  the  foundation  walls,  and 
the  connection  shall  be  made  by  soldering,  if  possible.     In  the  absence  of  other 
good  ground,  the  ground  shall  be  made  by  means  of  a  metallic  plate  or  a  bunch 
of  wires  buried  in  a  permanently  moist  earth.  • 

e.  The  metallic  sheathes  to  cables  must  be  permanently  and 
effectively  connected  to  "earth." 

f.  The  following  formula  for  soldering  fluid  is  suggested  :— 

Saturated  solution  of  zinc 5  parts 

Alcohol 4  parts 

Glycerine i  part 

WIRES. 

The  following  is  a  list  of  wires  which  have  been  tested  and 
found  to  comply  with  the  standard  for  approved  wires,  required 
for  all  high-potential  work  (300  volts  or  over);  and  for  service 
wires,  all  classes  of  concealed  wiring  and  wiring  exposed  to  damp- 
ness in  low  potential  work  : — 

Name  of  Wire.  Manufacturer. 

Americanite American  Electrical  Works. 

Bishop    Bishop  Gutta  Percha  Co. 

Clark , , Eastern  Electric  Cable  Co. 

Climax Simplex  Electric  Co. 

Simplex  (caoutchouc) Simplex  Electric  Co. 

Crescent    John  A.  Roebling's  Sons  Co. 

Crown Washburn  &  Moen. 

Globe Washburn  &  Moen. 

Salamander Washburn  &  Moen. 

Crefeld Crefeld  Electrical  Works. 

Grimshaw  (White  core) N.  Y.  Insulated  Wire  Co. 

Raven  core N.  Y.  Insulated  Wire  Co. 

Requa  (White  core)  Safety  Insulated  Wire  &  Cable  Co. 

Safety  (Black  core)  Safety  Insulated  Wire  &  Cable  Co. 

Habirshaw  (White  core) Ind.  Rubber  &  Gutta  Percha  Ins.  Co. 

Habirshaw  (Blue  core) Ind.  Rubber  &  Gutta  Percha  Ins.  Co. 

Habirshaw  (Red  core) Ind.  Rubber  &  Gutta  Percha  Ins.  Co. 

Paranite Indiana  Rubber  &  Insulated  Wire  Co. 

Liberty Atlas  Covering  Works. 

Kerite W.  R.  Brixey. 

( )konite Okonite  Co. 

Paracore    Nat.  India  Rubber  Co. 

N.  I.  R Nat.  India  Rubber  Co. 

U.  S Gen.  Electric  Co. 

Columbia C   S.  Knowles. 

NOTE. —The  results  of  recent  tests  on  these  and  other  wires  can  be  seen  at 
inspection  offices. 


222  RULES    AND    REQUIREMENTS. 

MATERIALS. 

The  following  are  given  as  a  list  of  NON-COMBUSTIBLE,  NON- 
ABSORPTIVE,  INSULATING  materials,  and  are  listed  here  for  the 
benefit  of  those  who  might  consider  hard  rubber,  fiber,  wood  and 
the  like  as  fulfilling  the  above  requirements.  Any  other  sub- 
stance, which  it  is  claimed  should  be  accepted,  must  be  forwarded 
for  testing  before  being  put  on  the  market: — 

1.  Glass. 

2.  Marble  (filled). 

3.  Slate  without  metal  veins. 

4.  Porcelain,  thoroughly  glazed  and  vitrified. 

5.  Pure  Sheet  Mica. 

6.  Lava  (certain  kinds  of). 

7.  Alberene  stone. 


10 


